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tx8jsd">.css-tx8jsd{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;}</style><a class="MuiTypography-root MuiTypography-body1 css-tx8jsd" target="_blank" href="https://docs.pingcap.com/" style="text-decoration:none;width:100%;color:inherit"><style data-emotion="css 1gesgke">.css-1gesgke .MuiTreeItem-content{color:#282a36;border-radius:4px;}.css-1gesgke .MuiTreeItem-content:hover{background-color:#f9f9f9;}.css-1gesgke .MuiTreeItem-content.Mui-selected,.css-1gesgke .MuiTreeItem-content.Mui-selected.Mui-focused{background-color:var(--tree-view-bg-color, #EAF6FB);color:var(--tree-view-color, #0A85C2);}.css-1gesgke .MuiTreeItem-content.Mui-selected svg.MuiTreeItem-ChevronRightIcon,.css-1gesgke .MuiTreeItem-content.Mui-selected.Mui-focused svg.MuiTreeItem-ChevronRightIcon{fill:var(--tree-view-color, #0A85C2);}.css-1gesgke .MuiTreeItem-content.Mui-focused{background-color:#f9f9f9;}.css-1gesgke 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0.12);}.css-khel7y.Mui-selected{background-color:rgba(25, 118, 210, 0.08);}.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.12);}@media (hover: none){.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.08);}}.css-khel7y.Mui-selected.Mui-focused{background-color:rgba(25, 118, 210, 0.2);}.css-khel7y .MuiTreeItem-iconContainer{margin-right:4px;width:15px;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;}.css-khel7y .MuiTreeItem-iconContainer svg{font-size:18px;}.css-khel7y .MuiTreeItem-label{width:100%;min-width:0;padding-left:4px;position:relative;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;}</style><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css znl8a3">.css-znl8a3{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;min-height:1.75rem;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;padding-left:0rem;padding-top:0.25rem;padding-bottom:0.25rem;}</style><div class="css-znl8a3"><style data-emotion="css 8atqhb">.css-8atqhb{width:100%;}</style><div class="MuiBox-root css-8atqhb"><style data-emotion="css 1hwyipb">.css-1hwyipb{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;color:inherit;font-size:0.875rem;line-height:1.25rem;}</style><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Docs Home</div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" 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class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Deploy</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-5" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Migrate</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium 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class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Monitor and Alert</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Troubleshoot</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" 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css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL Optimization Process</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-10-2-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Control Execution Plans</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-171pefp" focusable="false" aria-hidden="true" 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css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Optimizer Hints</div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/sql-plan-management"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-10-2-3-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-5fc025"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL Plan Management</div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/blocklist-control-plan"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-10-2-3-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-5fc025"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">The Blocklist of Optimization Rules and Expression Pushdown</div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/optimizer-fix-controls"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-10-2-3-4" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-5fc025"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Optimizer Fix Controls</div></div></div></div></div></li></a></div></div></ul></li></div></div></ul></li></div></div></ul></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Tutorials</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">TiDB Tools</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Reference</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium 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aria-expanded="false" id="left-nav-treeview-0-15" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Release Notes</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/glossary"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-16" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Glossary</div></div></div></div></div></li></a></ul></div></aside><style data-emotion="css sb2sd0">.css-sb2sd0{width:100%;}@media (min-width:1200px){.css-sb2sd0{max-width:calc(100% - 18.75rem);}}</style><main class="MuiBox-root css-sb2sd0"><style data-emotion="css 1rnnmjb">.css-1rnnmjb{max-width:1340px;width:100%;margin-left:auto;margin-right:auto;display:block;box-sizing:border-box;}</style><div class="MuiBox-root css-1rnnmjb"><style data-emotion="css 90fn5w">.css-90fn5w{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;}@media (min-width:0px){.css-90fn5w{-webkit-flex-direction:column-reverse;-ms-flex-direction:column-reverse;flex-direction:column-reverse;}}@media (min-width:600px){.css-90fn5w{-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;}}</style><div class="css-90fn5w"><style data-emotion="css vofosd">.css-vofosd{padding:1.5rem 0;}@media (min-width:0px){.css-vofosd{width:100%;}}@media (min-width:600px){.css-vofosd{width:calc(100% - 17.5rem);}}</style><div class="MuiBox-root css-vofosd"><style data-emotion="css 1ekb41w">.css-1ekb41w{width:100%;margin-left:auto;box-sizing:border-box;margin-right:auto;display:block;padding-left:16px;padding-right:16px;}@media (min-width:600px){.css-1ekb41w{padding-left:24px;padding-right:24px;}}@media (min-width:1536px){.css-1ekb41w{max-width:1536px;}}</style><div class="MuiContainer-root MuiContainer-maxWidthXl doc-content css-1ekb41w"><div class="markdown-body MuiBox-root css-0"><h1 id="optimizer-hints" style="position:relative"><a href="#optimizer-hints" aria-label="optimizer hints permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Optimizer Hints</h1><p>TiDB supports optimizer hints, which are based on the comment-like syntax introduced in MySQL 5.7. For example, one of the common syntaxes is <code>/*+ HINT_NAME([t1_name [, t2_name] ...]) */</code>. Use of optimizer hints is recommended in cases where the TiDB optimizer selects a less optimal query plan.</p><p>If you encounter a situation where hints do not take effect, see <a href="#troubleshoot-common-issues-that-hints-do-not-take-effect">Troubleshoot common issues that hints do not take effect</a>.</p><h2 id="syntax" style="position:relative"><a href="#syntax" aria-label="syntax permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Syntax</h2><p>Optimizer hints are case insensitive and specified within <code>/*+ ... */</code> comments following the <code>SELECT</code>, <code>INSERT</code>, <code>UPDATE</code> or <code>DELETE</code> keyword in a SQL statement.</p><p>Multiple hints can be specified by separating with commas. For example, the following query uses three different hints:</p><pre><code class="hljs language-sql"><style data-emotion="css 1qhimia">.css-1qhimia{margin-right:3rem;overflow:auto;}</style><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t1, idx1), HASH_AGG(), HASH_JOIN(t1) */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.b; </div><style data-emotion="css ux9q70">.css-ux9q70{text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:2.4rem;background:transparent;border:unset;}.css-ux9q70:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-ux9q70:hover{background-color:transparent;}}.css-ux9q70.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><style data-emotion="css 1rmx1rm">.css-1rmx1rm{display:-webkit-inline-box;display:-webkit-inline-flex;display:-ms-inline-flexbox;display:inline-flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;position:relative;box-sizing:border-box;-webkit-tap-highlight-color:transparent;background-color:transparent;outline:0;border:0;margin:0;border-radius:0;padding:0;cursor:pointer;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;vertical-align:middle;-moz-appearance:none;-webkit-appearance:none;-webkit-text-decoration:none;text-decoration:none;color:inherit;text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:2.4rem;background:transparent;border:unset;}.css-1rmx1rm::-moz-focus-inner{border-style:none;}.css-1rmx1rm.Mui-disabled{pointer-events:none;cursor:default;}@media print{.css-1rmx1rm{-webkit-print-color-adjust:exact;color-adjust:exact;}}.css-1rmx1rm:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-1rmx1rm:hover{background-color:transparent;}}.css-1rmx1rm.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><style data-emotion="css 1cw4hi4">.css-1cw4hi4{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:inherit;}</style><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><style data-emotion="css 1e2dcm1">.css-1e2dcm1{z-index:1500;pointer-events:none;}</style><style data-emotion="css okvapm">.css-okvapm{z-index:1500;pointer-events:none;}</style><style data-emotion="css rnn29l">.css-rnn29l{text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:0.625rem;background:transparent;border:unset;}.css-rnn29l:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-rnn29l:hover{background-color:transparent;}}.css-rnn29l.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><style data-emotion="css fxo539">.css-fxo539{display:-webkit-inline-box;display:-webkit-inline-flex;display:-ms-inline-flexbox;display:inline-flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;position:relative;box-sizing:border-box;-webkit-tap-highlight-color:transparent;background-color:transparent;outline:0;border:0;margin:0;border-radius:0;padding:0;cursor:pointer;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;vertical-align:middle;-moz-appearance:none;-webkit-appearance:none;-webkit-text-decoration:none;text-decoration:none;color:inherit;text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:0.625rem;background:transparent;border:unset;}.css-fxo539::-moz-focus-inner{border-style:none;}.css-fxo539.Mui-disabled{pointer-events:none;cursor:default;}@media print{.css-fxo539{-webkit-print-color-adjust:exact;color-adjust:exact;}}.css-fxo539:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-fxo539:hover{background-color:transparent;}}.css-fxo539.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>How optimizer hints affect query execution plans can be observed in the output of <a href="/tidb/stable/sql-statement-explain"><code>EXPLAIN</code></a> and <a href="/tidb/stable/sql-statement-explain-analyze"><code>EXPLAIN ANALYZE</code></a>.</p><p>An incorrect or incomplete hint will not result in a statement error. This is because hints are intended to have only a <em>hint</em> (suggestion) semantic to query execution. Similarly, TiDB will at most return a warning if a hint is not applicable.</p><style data-emotion="css 1weqspv">.css-1weqspv{padding-top:0.5rem;padding-bottom:0.5rem;}.css-1weqspv .MuiAlert-message p{margin-bottom:0px;margin-top:0px;}</style><div class="MuiBox-root css-1weqspv"><style data-emotion="css 17zlexa">.css-17zlexa{font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(1, 67, 97);background-color:rgb(229, 246, 253);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-17zlexa .MuiAlert-icon{color:#03a9f4;}</style><style data-emotion="css 152gid5">.css-152gid5{background-color:#fff;color:rgba(0, 0, 0, 0.87);-webkit-transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;border-radius:4px;box-shadow:none;font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(1, 67, 97);background-color:rgb(229, 246, 253);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-152gid5 .MuiAlert-icon{color:#03a9f4;}</style><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><style data-emotion="css 1l54tgj">.css-1l54tgj{margin-right:12px;padding:7px 0;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;font-size:22px;opacity:0.9;}</style><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><style data-emotion="css 1xsto0d">.css-1xsto0d{padding:8px 0;min-width:0;overflow:auto;}</style><div class="MuiAlert-message css-1xsto0d"><style data-emotion="css 1h2y6o4">.css-1h2y6o4{font-weight:500;margin-top:-2px;}</style><style data-emotion="css 17ioyuk">.css-17ioyuk{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;margin-bottom:0.35em;font-weight:500;margin-top:-2px;}</style><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>If the comments do not follow behind the specified keywords, they will be treated as common MySQL comments. The comments do not take effect, and no warning is reported.</p></div></div></div><p>Currently, TiDB supports two categories of hints, which are different in scope. The first category of hints takes effect in the scope of query blocks, such as <a href="#hash_agg"><code>/*+ HASH_AGG() */</code></a>; the second category of hints takes effect in the whole query, such as <a href="#memory_quotan"><code>/*+ MEMORY_QUOTA(1024 MB)*/</code></a>.</p><p>Each query or sub-query in a statement corresponds to a different query block, and each query block has its own name. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t1, (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The above query statement has three query blocks: the outermost <code>SELECT</code> corresponds to the first query block, whose name is <code>sel_1</code>; the two <code>SELECT</code> sub-queries correspond to the second and the third query block, whose names are <code>sel_2</code> and <code>sel_3</code>, respectively. The sequence of the numbers is based on the appearance of <code>SELECT</code> from left to right. If you replace the first <code>SELECT</code> with <code>DELETE</code> or <code>UPDATE</code>, then the corresponding query block names are <code>del_1</code> or <code>upd_1</code>.</p><h2 id="hints-that-take-effect-in-query-blocks" style="position:relative"><a href="#hints-that-take-effect-in-query-blocks" aria-label="hints that take effect in query blocks permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints that take effect in query blocks</h2><p>This category of hints can follow behind <strong>any</strong> <code>SELECT</code>, <code>UPDATE</code> or <code>DELETE</code> keywords. To control the effective scope of the hint, use the name of the query block in the hint. You can make the hint parameters clear by accurately identifying each table in the query (in case of duplicated table names or aliases). If no query block is specified in the hint, the hint takes effect in the current block by default.</p><p>For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN(@sel_1 t1@sel_1, t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> t1.a, t1.b <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.a) t1, t t3 <span class="hljs-keyword">WHERE</span> t1.b <span class="hljs-operator">=</span> t3.b; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>This hint takes effect in the <code>sel_1</code> query block, and its parameters are the <code>t1</code> and <code>t3</code> tables in <code>sel_1</code> (<code>sel_2</code> also contains a <code>t1</code> table).</p><p>As described above, you can specify the name of the query block in the hint in the following ways:</p><ul><li>Set the query block name as the first parameter of the hint, and separate it from other parameters with a space. In addition to <code>QB_NAME</code>, all the hints listed in this section also have another optional hidden parameter <code>@QB_NAME</code>. By using this parameter, you can specify the effective scope of this hint.</li><li>Append <code>@QB_NAME</code> to a table name in the parameter to explicitly specify which query block this table belongs to.</li></ul><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>You must put the hint in or before the query block where the hint takes effect. If the hint is put after the query block, it cannot take effect.</p></div></div></div><h3 id="qb_name" style="position:relative"><a href="#qb_name" aria-label="qb_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>QB_NAME</h3><p>If the query statement is a complicated statement that includes multiple nested queries, the ID and name of a certain query block might be mistakenly identified. The hint <code>QB_NAME</code> can help us in this regard.</p><p><code>QB_NAME</code> means Query Block Name. You can specify a new name to a query block. The specified <code>QB_NAME</code> and the previous default name are both valid. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(QB1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t1, (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>This hint specifies the outer <code>SELECT</code> query block's name to <code>QB1</code>, which makes <code>QB1</code> and the default name <code>sel_1</code> both valid for the query block.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>In the above example, if the hint specifies the <code>QB_NAME</code> to <code>sel_2</code> and does not specify a new <code>QB_NAME</code> for the original second <code>SELECT</code> query block, then <code>sel_2</code> becomes an invalid name for the second <code>SELECT</code> query block.</p></div></div></div><h3 id="set_varvar_namevar_value" style="position:relative"><a href="#set_varvar_namevar_value" aria-label="set_varvar_namevar_value permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>SET_VAR(VAR_NAME=VAR_VALUE)</h3><p>You can temporarily modify the value of system variables during statement execution by using the <code>SET_VAR(VAR_NAME=VAR_VALUE)</code> hint. After the statement is executed, the value of the system variable in the current session is automatically restored to the original value. This hint can be used to modify some system variables related to the optimizer and executor. For a list of system variables that can be modified using this hint, refer to <a href="/tidb/stable/system-variables">System variables</a>.</p><div class="MuiBox-root css-1weqspv"><style data-emotion="css 1rl2db2">.css-1rl2db2{font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(95, 33, 32);background-color:rgb(253, 237, 237);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-1rl2db2 .MuiAlert-icon{color:#ef5350;}</style><style data-emotion="css 21rxh6">.css-21rxh6{background-color:#fff;color:rgba(0, 0, 0, 0.87);-webkit-transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;border-radius:4px;box-shadow:none;font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(95, 33, 32);background-color:rgb(253, 237, 237);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-21rxh6 .MuiAlert-icon{color:#ef5350;}</style><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardError MuiAlert-standard css-21rxh6" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ErrorOutlineIcon"><path d="M11 15h2v2h-2zm0-8h2v6h-2zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Warning</div><p>It is strongly recommended not to modify variables that are not explicitly supported, as this might cause unpredictable behavior.</p></div></div></div><p>The following is an example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SET_VAR(MAX_EXECUTION_TIME=1234) */</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME; <span class="hljs-keyword">SELECT</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>After executing the preceding SQL statements, the first query returns the value <code>1234</code> set in the hint, instead of the default value of <code>MAX_EXECUTION_TIME</code>. The second query returns the default value of the variable.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">1234</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="merge_joint1_name--tl_name-" style="position:relative"><a href="#merge_joint1_name--tl_name-" aria-label="merge_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MERGE_JOIN(t1_name [, tl_name ...])</h3><p>The <code>MERGE_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer to use the sort-merge join algorithm for the given table(s). Generally, this algorithm consumes less memory but takes longer processing time. If there is a very large data volume or insufficient system memory, it is recommended to use this hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ MERGE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1, t2 <span class="hljs-keyword">where</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p><code>TIDB_SMJ</code> is the alias for <code>MERGE_JOIN</code> in TiDB 3.0.x and earlier versions. If you are using any of these versions, you must apply the <code>TIDB_SMJ(t1_name [, tl_name ...])</code> syntax for the hint. For the later versions of TiDB, <code>TIDB_SMJ</code> and <code>MERGE_JOIN</code> are both valid names for the hint, but <code>MERGE_JOIN</code> is recommended.</p></div></div></div><h3 id="no_merge_joint1_name--tl_name-" style="position:relative"><a href="#no_merge_joint1_name--tl_name-" aria-label="no_merge_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_MERGE_JOIN(t1_name [, tl_name ...])</h3><p>The <code>NO_MERGE_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer not to use the sort-merge join algorithm for the given table(s). For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_MERGE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="inl_joint1_name--tl_name-" style="position:relative"><a href="#inl_joint1_name--tl_name-" aria-label="inl_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>INL_JOIN(t1_name [, tl_name ...])</h3><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>In some cases, the <code>INL_JOIN</code> hint might not take effect. For more information, see <a href="#inl_join-hint-does-not-take-effect"><code>INL_JOIN</code> hint does not take effect</a>.</p></div></div></div><p>The <code>INL_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer to use the index nested loop join algorithm for the given table(s). This algorithm might consume less system resources and take shorter processing time in some scenarios and might produce an opposite result in other scenarios. If the result set is less than 10,000 rows after the outer table is filtered by the <code>WHERE</code> condition, it is recommended to use this hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In the preceding SQL statement, the <code>INL_JOIN(t1, t2)</code> hint tells the optimizer to use the index nested loop join algorithm for <code>t1</code> and <code>t2</code>. Note that this does not mean that the index nested loop join algorithm is used between <code>t1</code> and <code>t2</code>. Instead, the hint indicates that <code>t1</code> and <code>t2</code> each use the index nested loop join algorithm with another table (<code>t3</code>).</p><p>The parameter(s) given in <code>INL_JOIN()</code> is the candidate table for the inner table when you create the query plan. For example, <code>INL_JOIN(t1)</code> means that TiDB only considers using <code>t1</code> as the inner table to create a query plan. If the candidate table has an alias, you must use the alias as the parameter in <code>INL_JOIN()</code>; if it does not have an alias, use the table's original name as the parameter. For example, in the <code>select /*+ INL_JOIN(t1) */ * from t t1, t t2 where t1.a = t2.b;</code> query, you must use the <code>t</code> table's alias <code>t1</code> or <code>t2</code> rather than <code>t</code> as <code>INL_JOIN()</code>'s parameter.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p><code>TIDB_INLJ</code> is the alias for <code>INL_JOIN</code> in TiDB 3.0.x and earlier versions. If you are using any of these versions, you must apply the <code>TIDB_INLJ(t1_name [, tl_name ...])</code> syntax for the hint. For the later versions of TiDB, <code>TIDB_INLJ</code> and <code>INL_JOIN</code> are both valid names for the hint, but <code>INL_JOIN</code> is recommended.</p></div></div></div><h3 id="no_index_joint1_name--tl_name-" style="position:relative"><a href="#no_index_joint1_name--tl_name-" aria-label="no_index_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_INDEX_JOIN(t1_name [, tl_name ...])</h3><p>The <code>NO_INDEX_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer not to use the index nested loop join algorithm for the given table(s). For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_INDEX_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="inl_hash_join" style="position:relative"><a href="#inl_hash_join" aria-label="inl_hash_join permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>INL_HASH_JOIN</h3><p>The <code>INL_HASH_JOIN(t1_name [, tl_name])</code> hint tells the optimizer to use the index nested loop hash join algorithm. The conditions for using this algorithm are the same with the conditions for using the index nested loop join algorithm. The difference between the two algorithms is that <code>INL_JOIN</code> creates a hash table on the joined inner table, but <code>INL_HASH_JOIN</code> creates a hash table on the joined outer table. <code>INL_HASH_JOIN</code> has a fixed limit on memory usage, while the memory used by <code>INL_JOIN</code> depends on the number of rows matched in the inner table.</p><h3 id="no_index_hash_joint1_name--tl_name-" style="position:relative"><a href="#no_index_hash_joint1_name--tl_name-" aria-label="no_index_hash_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_INDEX_HASH_JOIN(t1_name [, tl_name ...])</h3><p>The <code>NO_INDEX_HASH_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer not to use the index nested loop hash join algorithm for the given table(s).</p><h3 id="inl_merge_join" style="position:relative"><a href="#inl_merge_join" aria-label="inl_merge_join permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>INL_MERGE_JOIN</h3><p>The <code>INL_MERGE_JOIN(t1_name [, tl_name])</code> hint tells the optimizer to use the index nested loop merge join algorithm. The conditions for using this algorithm are the same with the conditions for using the index nested loop join algorithm.</p><h3 id="no_index_merge_joint1_name--tl_name-" style="position:relative"><a href="#no_index_merge_joint1_name--tl_name-" aria-label="no_index_merge_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_INDEX_MERGE_JOIN(t1_name [, tl_name ...])</h3><p>The <code>NO_INDEX_MERGE_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer not to use the index nested loop merge join algorithm for the given table(s).</p><h3 id="hash_joint1_name--tl_name-" style="position:relative"><a href="#hash_joint1_name--tl_name-" aria-label="hash_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>HASH_JOIN(t1_name [, tl_name ...])</h3><p>The <code>HASH_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer to use the hash join algorithm for the given table(s). This algorithm allows the query to be executed concurrently with multiple threads, which achieves a higher processing speed but consumes more memory. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ HASH_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1, t2 <span class="hljs-keyword">where</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p><code>TIDB_HJ</code> is the alias for <code>HASH_JOIN</code> in TiDB 3.0.x and earlier versions. If you are using any of these versions, you must apply the <code>TIDB_HJ(t1_name [, tl_name ...])</code> syntax for the hint. For the later versions of TiDB, <code>TIDB_HJ</code> and <code>HASH_JOIN</code> are both valid names for the hint, but <code>HASH_JOIN</code> is recommended.</p></div></div></div><h3 id="no_hash_joint1_name--tl_name-" style="position:relative"><a href="#no_hash_joint1_name--tl_name-" aria-label="no_hash_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_HASH_JOIN(t1_name [, tl_name ...])</h3><p>The <code>NO_HASH_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer not to use the hash join algorithm for the given table(s). For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_HASH_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="hash_join_buildt1_name--tl_name-" style="position:relative"><a href="#hash_join_buildt1_name--tl_name-" aria-label="hash_join_buildt1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>HASH_JOIN_BUILD(t1_name [, tl_name ...])</h3><p>The <code>HASH_JOIN_BUILD(t1_name [, tl_name ...])</code> hint tells the optimizer to use the hash join algorithm on specified tables with these tables working as the build side. In this way, you can build hash tables using specific tables. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN_BUILD(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="hash_join_probet1_name--tl_name-" style="position:relative"><a href="#hash_join_probet1_name--tl_name-" aria-label="hash_join_probet1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>HASH_JOIN_PROBE(t1_name [, tl_name ...])</h3><p>The <code>HASH_JOIN_PROBE(t1_name [, tl_name ...])</code> hint tells the optimizer to use the hash join algorithm on specified tables with these tables working as the probe side. In this way, you can execute the hash join algorithm with specific tables as the probe side. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN_PROBE(t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="semi_join_rewrite" style="position:relative"><a href="#semi_join_rewrite" aria-label="semi_join_rewrite permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>SEMI_JOIN_REWRITE()</h3><p>The <code>SEMI_JOIN_REWRITE()</code> hint tells the optimizer to rewrite the semi-join query to an ordinary join query. Currently, this hint only works for <code>EXISTS</code> subqueries.</p><p>If this hint is not used to rewrite the query, when the hash join is selected in the execution plan, the semi-join query can only use the subquery to build a hash table. In this case, when the result of the subquery is bigger than that of the outer query, the execution speed might be slower than expected.</p><p>Similarly, when the index join is selected in the execution plan, the semi-join query can only use the outer query as the driving table. In this case, when the result of the subquery is smaller than that of the outer query, the execution speed might be slower than expected.</p><p>When <code>SEMI_JOIN_REWRITE()</code> is used to rewrite the query, the optimizer can extend the selection range to select a better execution plan.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Does not use SEMI_JOIN_REWRITE() to rewrite the query.</span> EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> <span class="hljs-keyword">EXISTS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-number">1</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t.a); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> <span class="hljs-operator">|</span> MergeJoin_9 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> semi <span class="hljs-keyword">join</span>, <span class="hljs-keyword">left</span> key:test.t.a, <span class="hljs-keyword">right</span> key:test.t1.a <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexReader_25(Build) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_24 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_24 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_23(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_22 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_22 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Uses SEMI_JOIN_REWRITE() to rewrite the query.</span> EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> <span class="hljs-keyword">EXISTS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SEMI_JOIN_REWRITE() */</span> <span class="hljs-number">1</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t.a); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_16 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:IndexReader_15, <span class="hljs-keyword">outer</span> key:test.t1.a, <span class="hljs-keyword">inner</span> key:test.t.a, equal cond:eq(test.t1.a, test.t.a) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─StreamAgg_39(Build) <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t1.a, funcs:firstrow(test.t1.a)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span>test.t1.a <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexReader_34 <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:Selection_14 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Selection_14 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t.a)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexRangeScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:idx(a) <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t.a, test.t1.a)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>From the preceding example, you can see that when using the <code>SEMI_JOIN_REWRITE()</code> hint, TiDB can select the execution method of IndexJoin based on the driving table <code>t1</code>.</p><h3 id="shuffle_joint1_name--tl_name-" style="position:relative"><a href="#shuffle_joint1_name--tl_name-" aria-label="shuffle_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>SHUFFLE_JOIN(t1_name [, tl_name ...])</h3><p>The <code>SHUFFLE_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer to use the Shuffle Join algorithm on specified tables. This hint only takes effect in the MPP mode. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SHUFFLE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li>Before using this hint, make sure that the current TiDB cluster can support using TiFlash MPP mode in the query. For details, refer to <a href="/tidb/stable/use-tiflash-mpp-mode">Use TiFlash MPP Mode</a>.</li><li>This hint can be used in combination with the <a href="#hash_join_buildt1_name--tl_name-"><code>HASH_JOIN_BUILD</code> hint</a> and <a href="#hash_join_probet1_name--tl_name-"><code>HASH_JOIN_PROBE</code> hint</a> to control the Build side and Probe side of the Shuffle Join algorithm.</li></ul></div></div></div><h3 id="broadcast_joint1_name--tl_name-" style="position:relative"><a href="#broadcast_joint1_name--tl_name-" aria-label="broadcast_joint1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>BROADCAST_JOIN(t1_name [, tl_name ...])</h3><p><code>BROADCAST_JOIN(t1_name [, tl_name ...])</code> hint tells the optimizer to use the Broadcast Join algorithm on specified tables. This hint only takes effect in the MPP mode. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ BROADCAST_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li>Before using this hint, make sure that the current TiDB cluster can support using TiFlash MPP mode in the query. For details, refer to <a href="/tidb/stable/use-tiflash-mpp-mode">Use TiFlash MPP Mode</a>.</li><li>This hint can be used in combination with the <a href="#hash_join_buildt1_name--tl_name-"><code>HASH_JOIN_BUILD</code> hint</a> and <a href="#hash_join_probet1_name--tl_name-"><code>HASH_JOIN_PROBE</code> hint</a> to control the Build side and Probe side of the Broadcast Join algorithm.</li></ul></div></div></div><h3 id="no_decorrelate" style="position:relative"><a href="#no_decorrelate" aria-label="no_decorrelate permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_DECORRELATE()</h3><p>The <code>NO_DECORRELATE()</code> hint tells the optimizer not to try to perform decorrelation for the correlated subquery in the specified query block. This hint is applicable to the <code>EXISTS</code>, <code>IN</code>, <code>ANY</code>, <code>ALL</code>, <code>SOME</code> subqueries and scalar subqueries that contain correlated columns (that is, correlated subqueries).</p><p>When this hint is used in a query block, the optimizer will not try to perform decorrelation for the correlated columns between the subquery and its outer query block, but always use the Apply operator to execute the query.</p><p>By default, TiDB tries to <a href="/tidb/stable/correlated-subquery-optimization">perform decorrelation</a> for correlated subqueries to achieve higher execution efficiency. However, in <a href="/tidb/stable/correlated-subquery-optimization#restrictions">some scenarios</a>, decorrelation might actually reduce the execution efficiency. In this case, you can use this hint to manually tell the optimizer not to perform decorrelation. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> t1(a <span class="hljs-type">int</span>, b <span class="hljs-type">int</span>); <span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> t2(a <span class="hljs-type">int</span>, b <span class="hljs-type">int</span>, index idx(b)); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Not using NO_DECORRELATE().</span> explain <span class="hljs-keyword">select</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&lt;</span> (<span class="hljs-keyword">select</span> <span class="hljs-built_in">sum</span>(t2.a) <span class="hljs-keyword">from</span> t2 <span class="hljs-keyword">where</span> t2.b <span class="hljs-operator">=</span> t1.b); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_11 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.b, test.t2.b)], other cond:lt(<span class="hljs-built_in">cast</span>(test.t1.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>), <span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─HashAgg_23(Build) <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t2.b, funcs:<span class="hljs-built_in">sum</span>(<span class="hljs-keyword">Column</span>#<span class="hljs-number">8</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>, funcs:firstrow(test.t2.b)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span>test.t2.b <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_24 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:HashAgg_16 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─HashAgg_16 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t2.b, funcs:<span class="hljs-built_in">sum</span>(test.t2.a)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">8</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─Selection_22 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t2.b)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:Selection_14 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Selection_14 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t1.b)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>From the preceding execution plan, you can see that the optimizer has automatically performed decorrelation. The decorrelated execution plan does not have the Apply operator. Instead, the plan has join operations between the subquery and the outer query block. The original filter condition (<code>t2.b = t1.b</code>) with the correlated column becomes a regular join condition.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Using NO_DECORRELATE().</span> explain <span class="hljs-keyword">select</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&lt;</span> (<span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ NO_DECORRELATE() */</span> <span class="hljs-built_in">sum</span>(t2.a) <span class="hljs-keyword">from</span> t2 <span class="hljs-keyword">where</span> t2.b <span class="hljs-operator">=</span> t1.b); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Projection_10 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.a, test.t1.b <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Apply_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> CARTESIAN <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, other cond:lt(<span class="hljs-built_in">cast</span>(test.t1.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>), <span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_14(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─MaxOneRow_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─StreamAgg_20 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> funcs:<span class="hljs-built_in">sum</span>(<span class="hljs-keyword">Column</span>#<span class="hljs-number">14</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_45 <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-built_in">cast</span>(test.t2.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">14</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexLookUp_44 <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexRangeScan_42(Build) <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2, index:idx(b) <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t2.b, test.t1.b)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRowIDScan_43(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>From the preceding execution plan, you can see that the optimizer does not perform decorrelation. The execution plan still contains the Apply operator. The filter condition (<code>t2.b = t1.b</code>) with the correlated column is still the filter condition when accessing the <code>t2</code> table.</p><h3 id="hash_agg" style="position:relative"><a href="#hash_agg" aria-label="hash_agg permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>HASH_AGG()</h3><p>The <code>HASH_AGG()</code> hint tells the optimizer to use the hash aggregation algorithm in all the aggregate functions in the specified query block. This algorithm allows the query to be executed concurrently with multiple threads, which achieves a higher processing speed but consumes more memory. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ HASH_AGG() */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">from</span> t1, t2 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="stream_agg" style="position:relative"><a href="#stream_agg" aria-label="stream_agg permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>STREAM_AGG()</h3><p>The <code>STREAM_AGG()</code> hint tells the optimizer to use the stream aggregation algorithm in all the aggregate functions in the specified query block. Generally, this algorithm consumes less memory but takes longer processing time. If there is a very large data volume or insufficient system memory, it is recommended to use this hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ STREAM_AGG() */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">from</span> t1, t2 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="mpp_1phase_agg" style="position:relative"><a href="#mpp_1phase_agg" aria-label="mpp_1phase_agg permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MPP_1PHASE_AGG()</h3><p><code>MPP_1PHASE_AGG()</code> tells the optimizer to use the one-phase aggregation algorithm for all aggregate functions in the specified query block. This hint only takes effect in the MPP mode. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MPP_1PHASE_AGG() */</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>Before using this hint, make sure that the current TiDB cluster can support using TiFlash MPP mode in the query. For details, refer to <a href="/tidb/stable/use-tiflash-mpp-mode">Use TiFlash MPP Mode</a>.</p></div></div></div><h3 id="mpp_2phase_agg" style="position:relative"><a href="#mpp_2phase_agg" aria-label="mpp_2phase_agg permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MPP_2PHASE_AGG()</h3><p><code>MPP_2PHASE_AGG()</code> tells the optimizer to use the two-phase aggregation algorithm for all aggregate functions in the specified query block. This hint only takes effect in the MPP mode. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MPP_2PHASE_AGG() */</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>Before using this hint, make sure that the current TiDB cluster can support using TiFlash MPP mode in the query. For details, refer to <a href="/tidb/stable/use-tiflash-mpp-mode">Use TiFlash MPP Mode</a>.</p></div></div></div><h3 id="use_indext1_name-idx1_name--idx2_name-" style="position:relative"><a href="#use_indext1_name-idx1_name--idx2_name-" aria-label="use_indext1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>USE_INDEX(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>USE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to use only the given index(es) for a specified <code>t1_name</code> table. For example, applying the following hint has the same effect as executing the <code>select * from t t1 use index(idx1, idx2);</code> statement.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t1, idx1, idx2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>If you specify only the table name but not index name in this hint, the execution does not consider any index but scan the entire table.</p></div></div></div><h3 id="force_indext1_name-idx1_name--idx2_name-" style="position:relative"><a href="#force_indext1_name-idx1_name--idx2_name-" aria-label="force_indext1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to use only the given index(es).</p><p>The usage and effect of <code>FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> are the same as the usage and effect of <code>USE_INDEX(t1_name, idx1_name [, idx2_name ...])</code>.</p><p>The following 4 queries have the same effect:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t, idx1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ FORCE_INDEX(t, idx1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t use index(idx1); <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t force index(idx1); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="ignore_indext1_name-idx1_name--idx2_name-" style="position:relative"><a href="#ignore_indext1_name-idx1_name--idx2_name-" aria-label="ignore_indext1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>IGNORE_INDEX(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>IGNORE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to ignore the given index(es) for a specified <code>t1_name</code> table. For example, applying the following hint has the same effect as executing the <code>select * from t t1 ignore index(idx1, idx2);</code> statement.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ IGNORE_INDEX(t1, idx1, idx2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="order_indext1_name-idx1_name--idx2_name-" style="position:relative"><a href="#order_indext1_name-idx1_name--idx2_name-" aria-label="order_indext1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to use only the given index for a specified table and read the specified index in order.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardError MuiAlert-standard css-21rxh6" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ErrorOutlineIcon"><path d="M11 15h2v2h-2zm0-8h2v6h-2zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Warning</div><p>This hint might cause SQL statements to fail. It is recommended to test it first. If an error occurs during the test, remove the hint. If the test runs normally, you can continue using it.</p></div></div></div><p>This hint is usually applied in the following scenario:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t(a <span class="hljs-type">INT</span>, b <span class="hljs-type">INT</span>, key(a), key(b)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ ORDER_INDEX(t, a) */</span> a <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> a LIMIT <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> <span class="hljs-operator">|</span> Limit_10 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_14 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:Limit_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Limit_13 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:a(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The optimizer generates two types of plan for this query: <code>Limit + IndexScan(keep order: true)</code> and <code>TopN + IndexScan(keep order: false)</code>. When the <code>ORDER_INDEX</code> hint is used, the optimizer chooses the first plan that reads the index in order.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li>If the query itself does not need to read the index in order (that is, without a hint, the optimizer does not generate a plan that reads the index in order in any situation), when the <code>ORDER_INDEX</code> hint is used, the error <code>Can't find a proper physical plan for this query</code> occurs. In this case, you need to remove the corresponding <code>ORDER_INDEX</code> hint.</li><li>The index on a partitioned table cannot be read in order, so do not use the <code>ORDER_INDEX</code> hint on the partitioned table and its related indexes.</li></ul></div></div></div><h3 id="no_order_indext1_name-idx1_name--idx2_name-" style="position:relative"><a href="#no_order_indext1_name-idx1_name--idx2_name-" aria-label="no_order_indext1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>NO_ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to use only the given index for a specified table and not to read the specified index in order. This hint is usually applied in the following scenario.</p><p>The following example shows that the effect of the query statement is equivalent to <code>SELECT * FROM t t1 use index(idx1, idx2);</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t(a <span class="hljs-type">INT</span>, b <span class="hljs-type">INT</span>, key(a), key(b)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_ORDER_INDEX(t, a) */</span> a <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> a LIMIT <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> <span class="hljs-operator">|</span> TopN_7 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t.a, <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_14 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:TopN_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TopN_13 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t.a, <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:a(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The same as the example of <code>ORDER_INDEX</code> hint, the optimizer generates two types of plans for this query: <code>Limit + IndexScan(keep order: true)</code> and <code>TopN + IndexScan(keep order: false)</code>. When the <code>NO_ORDER_INDEX</code> hint is used, the optimizer will choose the latter plan to read the index out of order.</p><h3 id="agg_to_cop" style="position:relative"><a href="#agg_to_cop" aria-label="agg_to_cop permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>AGG_TO_COP()</h3><p>The <code>AGG_TO_COP()</code> hint tells the optimizer to push down the aggregate operation in the specified query block to the coprocessor. If the optimizer does not push down some aggregate function that is suitable for pushdown, then it is recommended to use this hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ AGG_TO_COP() */</span> <span class="hljs-built_in">sum</span>(t1.a) <span class="hljs-keyword">from</span> t t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="limit_to_cop" style="position:relative"><a href="#limit_to_cop" aria-label="limit_to_cop permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>LIMIT_TO_COP()</h3><p>The <code>LIMIT_TO_COP()</code> hint tells the optimizer to push down the <code>Limit</code> and <code>TopN</code> operators in the specified query block to the coprocessor. If the optimizer does not perform such an operation, it is recommended to use this hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LIMIT_TO_COP() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> a <span class="hljs-operator">=</span> <span class="hljs-number">1</span> <span class="hljs-keyword">AND</span> b <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> c LIMIT <span class="hljs-number">1</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="read_from_storagetiflasht1_name--tl_name--tikvt2_name--tl_name-" style="position:relative"><a href="#read_from_storagetiflasht1_name--tl_name--tikvt2_name--tl_name-" aria-label="read_from_storagetiflasht1_name tl_name tikvt2_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>READ_FROM_STORAGE(TIFLASH[t1_name [, tl_name ...]], TIKV[t2_name [, tl_name ...]])</h3><p>The <code>READ_FROM_STORAGE(TIFLASH[t1_name [, tl_name ...]], TIKV[t2_name [, tl_name ...]])</code> hint tells the optimizer to read specific table(s) from specific storage engine(s). Currently, this hint supports two storage engine parameters - <code>TIKV</code> and <code>TIFLASH</code>. If a table has an alias, use the alias as the parameter of <code>READ_FROM_STORAGE()</code>; if the table does not has an alias, use the table's original name as the parameter. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ READ_FROM_STORAGE(TIFLASH[t1], TIKV[t2]) */</span> t1.a <span class="hljs-keyword">from</span> t t1, t t2 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">=</span> t2.a; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="use_index_merget1_name-idx1_name--idx2_name-" style="position:relative"><a href="#use_index_merget1_name-idx1_name--idx2_name-" aria-label="use_index_merget1_name idx1_name idx2_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>USE_INDEX_MERGE(t1_name, idx1_name [, idx2_name ...])</h3><p>The <code>USE_INDEX_MERGE(t1_name, idx1_name [, idx2_name ...])</code> hint tells the optimizer to access a specific table with the index merge method. Index merge has two types: intersection type and union type. For details, see <a href="/tidb/stable/explain-index-merge">Explain Statements Using Index Merge</a>.</p><p>If you explicitly specify the list of indexes, TiDB selects indexes from the list to build index merge; if you do not specify the list of indexes, TiDB selects indexes from all available indexes to build index merge.</p><p>For the intersection-type index merge, the given list of indexes is a required parameter in the hint. For the union-type index merge, the given list of indexes is an optional parameter in the hint. See the following example.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX_MERGE(t1, idx_a, idx_b, idx_c) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">OR</span> t1.b <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>When multiple <code>USE_INDEX_MERGE</code> hints are made to the same table, the optimizer tries to select the index from the union of the index sets specified by these hints.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>The parameters of <code>USE_INDEX_MERGE</code> refer to index names, rather than column names. The index name of the primary key is <code>primary</code>.</p></div></div></div><h3 id="leadingt1_name--tl_name-" style="position:relative"><a href="#leadingt1_name--tl_name-" aria-label="leadingt1_name tl_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>LEADING(t1_name [, tl_name ...])</h3><p>The <code>LEADING(t1_name [, tl_name ...])</code> hint reminds the optimizer that, when generating the execution plan, to determine the order of multi-table joins according to the order of table names specified in the hint. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LEADING(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">and</span> t2.id <span class="hljs-operator">=</span> t3.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In the above query with multi-table joins, the order of joins is determined by the order of table names specified in the <code>LEADING()</code> hint. The optimizer will first join <code>t1</code> and <code>t2</code> and then join the result with <code>t3</code>. This hint is more general than <a href="#straight_join"><code>STRAIGHT_JOIN</code></a>.</p><p>The <code>LEADING</code> hint does not take effect in the following situations:</p><ul><li>Multiple <code>LEADING</code> hints are specified.</li><li>The table name specified in the <code>LEADING</code> hint does not exist.</li><li>A duplicated table name is specified in the <code>LEADING</code> hint.</li><li>The optimizer cannot perform join operations according to the order as specified by the <code>LEADING</code> hint.</li><li>The <code>straight_join()</code> hint already exists.</li><li>The query contains an outer join together with the Cartesian product.</li></ul><p>In the preceding situations, a warning is generated.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Multiple `LEADING` hints are specified.</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LEADING(t1, t2) LEADING(t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">and</span> t2.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-comment">-- To learn why the `LEADING` hint fails to take effect, execute `show warnings`.</span> <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> We can <span class="hljs-keyword">only</span> use <span class="hljs-keyword">one</span> <span class="hljs-keyword">leading</span> hint <span class="hljs-keyword">at</span> most, <span class="hljs-keyword">when</span> multiple <span class="hljs-keyword">leading</span> hints <span class="hljs-keyword">are</span> used, <span class="hljs-keyword">all</span> <span class="hljs-keyword">leading</span> hints will be invalid <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>If the query statement includes an outer join, in the hint you can specify only the tables whose join order can be swapped. If there is a table in the hint whose join order cannot be swapped, the hint will be invalid. For example, in <code>SELECT * FROM t1 LEFT JOIN (t2 JOIN t3 JOIN t4) ON t1.a = t2.a;</code>, if you want to control the join order of <code>t2</code>, <code>t3</code>, and <code>t4</code> tables, you cannot specify <code>t1</code> in the <code>LEADING</code> hint.</p></div></div></div><h3 id="merge" style="position:relative"><a href="#merge" aria-label="merge permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MERGE()</h3><p>Using the <code>MERGE()</code> hint in queries with common table expressions (CTE) can disable the materialization of the subqueries and expand the subquery inlines into CTE. This hint is only applicable to non-recursive CTE. In some scenarios, using <code>MERGE()</code> brings higher execution efficiency than the default behavior of allocating a temporary space. For example, pushing down query conditions or in nesting CTE queries:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- Uses the hint to push down the predicate of the outer query.</span> <span class="hljs-keyword">WITH</span> CTE <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> tc <span class="hljs-keyword">WHERE</span> tc.a <span class="hljs-operator">&lt;</span> <span class="hljs-number">60</span>) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE <span class="hljs-keyword">WHERE</span> CTE.a <span class="hljs-operator">&lt;</span> <span class="hljs-number">18</span>; <span class="hljs-comment">-- Uses the hint in a nested CTE query to expand a CTE inline into the outer query.</span> <span class="hljs-keyword">WITH</span> CTE1 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1), CTE2 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">WITH</span> CTE3 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t2), CTE4 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t3) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE3, CTE4) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE1, CTE2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p><code>MERGE()</code> is only applicable to simple CTE queries. It is not applicable in the following situations:</p><ul><li><a href="https://docs.pingcap.com/tidb/stable/dev-guide-use-common-table-expression#recursive-cte" target="_blank" referrerpolicy="no-referrer-when-downgrade">Recursive CTE</a></li><li>Subqueries with inlines that cannot be expanded, such as aggregate operators, window functions, and <code>DISTINCT</code>.</li></ul><p>When the number of CTE references is too high, the query performance might be lower than the default materialization behavior.</p></div></div></div><h2 id="hints-that-take-effect-globally" style="position:relative"><a href="#hints-that-take-effect-globally" aria-label="hints that take effect globally permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints that take effect globally</h2><p>The global hint works in <a href="/tidb/stable/views">views</a>. When specified as a global hint, the hint defined in a query can take effect inside the view. To specify a global hint, first use the <code>QB_NAME</code> hint to define a query block name, and then add the target hints in the form of <code>ViewName@QueryBlockName</code>.</p><h3 id="step-1-define-the-query-block-name-of-the-view-using-the-qb_name-hint" style="position:relative"><a href="#step-1-define-the-query-block-name-of-the-view-using-the-qb_name-hint" aria-label="step 1 define the query block name of the view using the qb_name hint permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Step 1: Define the query block name of the view using the <code>QB_NAME</code> hint</h3><p>Use the <a href="#qb_name"><code>QB_NAME</code> hint</a> to define a new name for each query block of the view. The definition of the <code>QB_NAME</code> hint for views is the same as that for <a href="#qb_name">query blocks</a>, but the syntax is extended from <code>QB_NAME(QB)</code> to <code>QB_NAME(QB, ViewName@QueryBlockName [.ViewName@QueryBlockName .ViewName@QueryBlockName ...])</code>.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>There is a white space between <code>@QueryBlockName</code> and the immediately following <code>.ViewName@QueryBlockName</code>. Otherwise, the <code>.ViewName@QueryBlockName</code> will be treated as a part of the <code>QueryBlockName</code>. For example, <code>QB_NAME(v2_1, v2@SEL_1 .@SEL_1)</code> is valid, while <code>QB_NAME(v2_1, v2@SEL_1.@SEL_1)</code> cannot be parsed correctly.</p></div></div></div><ul><li><p>For a simple statement with a single view and no subqueries, the following example specifies the first query block name of view <code>v</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* Comment: The name of the current query block is the default @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> For view <code>v</code>, the first view name in the list (<code>ViewName@QueryBlockName [.ViewName@QueryBlockName .ViewName@QueryBlockName ...]</code>) starting from the query statement is <code>v@SEL_1</code>. The first query block of the view <code>v</code> can be declared as <code>QB_NAME(v_1, v@SEL_1 .@SEL_1)</code>, or simply written as <code>QB_NAME(v_1, v)</code>, omitting <code>@SEL_1</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* Comment: The name of the current query block is the default @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-comment">-- Specifies the global hint</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v_1, v) USE_INDEX(t@v_1, idx) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>For a complex statement with nested views and subqueries, the following example specifies the names for each of two query blocks of the view <code>v1</code> and <code>v2</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* Comment: The name of the current query block is the default @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2 <span class="hljs-keyword">JOIN</span> ( <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* Comment: The name of the current query block is the default @SEL_2 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2) vv; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> For the first view <code>v2</code>, the first view name in the list starting from the first query statement is <code>v2@SEL_1</code>. For the second view <code>v2</code>, the first view name is <code>v2@SEL_2</code>. The following example only considers the first view <code>v2</code>.</p><p> The first query block of view <code>v2</code> can be declared as <code>QB_NAME(v2_1, v2@SEL_1 .@SEL_1)</code>, and the second query block of the view <code>v2</code> can be declared as <code>QB_NAME(v2_2, v2@SEL_1 .@SEL_2)</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v2 <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">JOIN</span> <span class="hljs-comment">/* Comment: For view v2, the name of the current query block is the default @SEL_1. So, the current query block view list is v2@SEL_1 .@SEL_1 */</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">JOIN</span> v1 <span class="hljs-comment">/* Comment: For view v2, the name of the current query block is the default @SEL_2. So, the current query block view list is v2@SEL_1 .@SEL_2 */</span> ) tt; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> For view <code>v1</code>, the first view name in the list starting from the preceding statement is <code>v2@SEL_1 .v1@SEL_2</code>. The first query block in view <code>v1</code> can be declared as <code>QB_NAME(v1_1, v2@SEL_1 .v1@SEL_2 .@SEL_1)</code>, and the second query block in view <code>v1</code> can be declared as <code>QB_NAME(v1_2, v2@SEL_1 .v1@SEL_2 .@SEL_2)</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v1 <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">JOIN</span> <span class="hljs-comment">/* Comment: For view `v1`, the name of the current query block is the default @SEL_1. So, the current query block view list is v2@SEL_1 .@SEL_2 .v1@SEL_1 */</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">JOIN</span> t2 <span class="hljs-comment">/* Comment: For view `v1`, the name of the current query block is the default @SEL_2. So, the current query block view list is v2@SEL_1 .@SEL_2 .v1@SEL_2 */</span> ) tt; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li></ul><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li><p>To use global hints with views, you must define the corresponding <code>QB_NAME</code> hints in the view. Otherwise, the global hints will not take effect.</p></li><li><p>When using a hint to specify multiple table names in a view, you need to ensure that the table names appearing in the same hint are in the same query block of the same view.</p></li><li><p>When you define the <code>QB_NAME</code> hint in a view for the outermost query block:</p><ul><li><p>For the first item of the view list in the <code>QB_NAME</code>, if the <code>@SEL_</code> is not explicitly declared, the default is consistent with the query block position where the <code>QB_NAME</code> is defined. That is, the query <code>SELECT /*+ QB_NAME(qb1, v2) */ * FROM v2 JOIN (SELECT /*+ QB_NAME(qb2, v2) */ * FROM v2) vv;</code> is equivalent to <code>SELECT /*+ QB_NAME(qb1, v2@SEL_1) */ * FROM v2 JOIN (SELECT /*+ QB_NAME(qb2, v2@SEL_2) */ * FROM v2) vv;</code>.</p></li><li><p>For items other than the first item of the view list in the <code>QB_NAME</code>, only <code>@SEL_1</code> can be omitted. That is, if <code>@SEL_1</code> is declared in the first query block of the current view, <code>@SEL_1</code> can be omitted. Otherwise, <code>@SEL_</code> cannot be omitted. For the preceding example:</p><ul><li>The first query block of the view <code>v2</code> can be declared as <code>QB_NAME(v2_1, v2)</code>.</li><li>The second query block of the view <code>v2</code> can be declared as <code>QB_NAME(v2_2, v2.@SEL_2)</code>.</li><li>The first query block of the view <code>v1</code> can be declared as <code>QB_NAME(v1_1, v2.v1@SEL_2)</code>.</li><li>The second query block of the view <code>v1</code> can be declared as <code>QB_NAME(v1_2, v2.v1@SEL_2 .@SEL_2)</code>.</li></ul></li></ul></li></ul></div></div></div><h3 id="step-2-add-the-target-hints" style="position:relative"><a href="#step-2-add-the-target-hints" aria-label="step 2 add the target hints permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Step 2: Add the target hints</h3><p>After defining the <code>QB_NAME</code> hint for query blocks of the view, you can add required <a href="#hints-that-take-effect-in-query-blocks">hints that take effect in query blocks</a> in the form of <code>ViewName@QueryBlockName</code> to make them effective inside the view. For example:</p><ul><li><p>Specify the <code>MERGE_JOIN()</code> hint for the first query block of the view <code>v2</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v2_1, v2) merge_join(t@v2_1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>Specify the <code>MERGE_JOIN()</code> and <code>STREAM_AGG()</code> hints for the second query block of the view <code>v2</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v2_2, v2.@SEL_2) merge_join(t1@v2_2) stream_agg(@v2_2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>Specify the <code>HASH_JOIN()</code> hint for the first query block of the view <code>v1</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v1_1, v2.v1@SEL_2) hash_join(t@v1_1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>Specify the <code>HASH_JOIN()</code> and <code>HASH_AGG()</code> hints for the second query block of the view <code>v1</code>:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v1_2, v2.v1@SEL_2 .@SEL_2) hash_join(t1@v1_2) hash_agg(@v1_2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li></ul><h2 id="hints-that-take-effect-in-the-whole-query" style="position:relative"><a href="#hints-that-take-effect-in-the-whole-query" aria-label="hints that take effect in the whole query permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints that take effect in the whole query</h2><p>This category of hints can only follow behind the <strong>first</strong> <code>SELECT</code>, <code>UPDATE</code> or <code>DELETE</code> keyword, which is equivalent to modifying the value of the specified system variable when this query is executed. The priority of the hint is higher than that of existing system variables.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p>This category of hints also has an optional hidden variable <code>@QB_NAME</code>, but the hint takes effect in the whole query even if you specify the variable.</p></div></div></div><h3 id="no_index_merge" style="position:relative"><a href="#no_index_merge" aria-label="no_index_merge permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NO_INDEX_MERGE()</h3><p>The <code>NO_INDEX_MERGE()</code> hint disables the index merge feature of the optimizer.</p><p>For example, the following query will not use index merge:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ NO_INDEX_MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t <span class="hljs-keyword">where</span> t.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">0</span> <span class="hljs-keyword">or</span> t.b <span class="hljs-operator">&gt;</span> <span class="hljs-number">0</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In addition to this hint, setting the <code>tidb_enable_index_merge</code> system variable also controls whether to enable this feature.</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li><code>NO_INDEX_MERGE</code> has a higher priority over <code>USE_INDEX_MERGE</code>. When both hints are used, <code>USE_INDEX_MERGE</code> does not take effect.</li><li>For a subquery, <code>NO_INDEX_MERGE</code> only takes effect when it is placed at the outermost level of the subquery.</li></ul></div></div></div><h3 id="use_tojaboolean_value" style="position:relative"><a href="#use_tojaboolean_value" aria-label="use_tojaboolean_value permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>USE_TOJA(boolean_value)</h3><p>The <code>boolean_value</code> parameter can be <code>TRUE</code> or <code>FALSE</code>. The <code>USE_TOJA(TRUE)</code> hint enables the optimizer to convert an <code>in</code> condition (containing a sub-query) to join and aggregation operations. Comparatively, the <code>USE_TOJA(FALSE)</code> hint disables this feature.</p><p>For example, the following query will convert <code>in (select t2.a from t2) subq</code> to corresponding join and aggregation operations:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ USE_TOJA(TRUE) */</span> t1.a, t1.b <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">where</span> t1.a <span class="hljs-keyword">in</span> (<span class="hljs-keyword">select</span> t2.a <span class="hljs-keyword">from</span> t2) subq; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In addition to this hint, setting the <code>tidb_opt_insubq_to_join_and_agg</code> system variable also controls whether to enable this feature.</p><h3 id="max_execution_timen" style="position:relative"><a href="#max_execution_timen" aria-label="max_execution_timen permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MAX_EXECUTION_TIME(N)</h3><p>The <code>MAX_EXECUTION_TIME(N)</code> hint places a limit <code>N</code> (a timeout value in milliseconds) on how long a statement is permitted to execute before the server terminates it. In the following hint, <code>MAX_EXECUTION_TIME(1000)</code> means that the timeout is 1000 milliseconds (that is, 1 second):</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ MAX_EXECUTION_TIME(1000) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span> t2 <span class="hljs-keyword">where</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In addition to this hint, the <code>global.max_execution_time</code> system variable can also limit the execution time of a statement.</p><h3 id="memory_quotan" style="position:relative"><a href="#memory_quotan" aria-label="memory_quotan permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>MEMORY_QUOTA(N)</h3><p>The <code>MEMORY_QUOTA(N)</code> hint places a limit <code>N</code> (a threshold value in MB or GB) on how much memory a statement is permitted to use. When a statement's memory usage exceeds this limit, TiDB produces a log message based on the statement's over-limit behavior or just terminates it.</p><p>In the following hint, <code>MEMORY_QUOTA(1024 MB)</code> means that the memory usage is limited to 1024 MB:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ MEMORY_QUOTA(1024 MB) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In addition to this hint, the <a href="/tidb/stable/system-variables#tidb_mem_quota_query"><code>tidb_mem_quota_query</code></a> system variable can also limit the memory usage of a statement.</p><h3 id="read_consistent_replica" style="position:relative"><a href="#read_consistent_replica" aria-label="read_consistent_replica permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>READ_CONSISTENT_REPLICA()</h3><p>The <code>READ_CONSISTENT_REPLICA()</code> hint enables the feature of reading consistent data from the TiKV follower node. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ READ_CONSISTENT_REPLICA() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In addition to this hint, setting the <code>tidb_replica_read</code> environment variable to <code>'follower'</code> or <code>'leader'</code> also controls whether to enable this feature.</p><h3 id="ignore_plan_cache" style="position:relative"><a href="#ignore_plan_cache" aria-label="ignore_plan_cache permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>IGNORE_PLAN_CACHE()</h3><p>The <code>IGNORE_PLAN_CACHE()</code> hint reminds the optimizer not to use the Plan Cache when handling the current <code>prepare</code> statement.</p><p>This hint is used to temporarily disable the Plan Cache for a certain type of queries when <a href="/tidb/stable/sql-prepared-plan-cache">prepare-plan-cache</a> is enabled.</p><p>In the following example, the Plan Cache is forcibly disabled when executing the <code>prepare</code> statement.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">prepare</span> stmt <span class="hljs-keyword">from</span> <span class="hljs-string">'select /*+ IGNORE_PLAN_CACHE() */ * from t where t.id = ?'</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="straight_join" style="position:relative"><a href="#straight_join" aria-label="straight_join permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>STRAIGHT_JOIN()</h3><p>The <code>STRAIGHT_JOIN()</code> hint reminds the optimizer to join tables in the order of table names in the <code>FROM</code> clause when generating the join plan.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ STRAIGHT_JOIN() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.a; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><ul><li><code>STRAIGHT_JOIN</code> has higher priority over <code>LEADING</code>. When both hints are used, <code>LEADING</code> does not take effect.</li><li>It is recommended to use the <code>LEADING</code> hint, which is more general than the <code>STRAIGHT_JOIN</code> hint.</li></ul></div></div></div><h3 id="nth_plann" style="position:relative"><a href="#nth_plann" aria-label="nth_plann permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>NTH_PLAN(N)</h3><p>The <code>NTH_PLAN(N)</code> hint reminds the optimizer to select the <code>N</code>th physical plan found during the physical optimization. <code>N</code> must be a positive integer.</p><p>If the specified <code>N</code> is beyond the search range of the physical optimization, TiDB will return a warning and select the optimal physical plan based on the strategy that ignores this hint.</p><p>This hint does not take effect when the cascades planner is enabled.</p><p>In the following example, the optimizer is forced to select the third physical plan found during the physical optimization:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NTH_PLAN(3) */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">from</span> t <span class="hljs-keyword">where</span> a <span class="hljs-operator">&gt;</span> <span class="hljs-number">5</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Note</div><p><code>NTH_PLAN(N)</code> is mainly used for testing, and its compatibility is not guaranteed in later versions. Use this hint <strong>with caution</strong>.</p></div></div></div><h3 id="resource_groupresource_group_name" style="position:relative"><a href="#resource_groupresource_group_name" aria-label="resource_groupresource_group_name permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>RESOURCE_GROUP(resource_group_name)</h3><p><code>RESOURCE_GROUP(resource_group_name)</code> is used for <a href="/tidb/stable/tidb-resource-control">Resource Control</a> to isolate resources. This hint temporarily executes the current statement using the specified resource group. If the specified resource group does not exist, this hint will be ignored.</p><p>Example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ RESOURCE_GROUP(rg1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t limit <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h2 id="troubleshoot-common-issues-that-hints-do-not-take-effect" style="position:relative"><a href="#troubleshoot-common-issues-that-hints-do-not-take-effect" aria-label="troubleshoot common issues that hints do not take effect permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Troubleshoot common issues that hints do not take effect</h2><h3 id="hints-do-not-take-effect-because-your-mysql-command-line-client-strips-hints" style="position:relative"><a href="#hints-do-not-take-effect-because-your-mysql-command-line-client-strips-hints" aria-label="hints do not take effect because your mysql command line client strips hints permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints do not take effect because your MySQL command-line client strips hints</h3><p>MySQL command-line clients earlier than 5.7.7 strip optimizer hints by default. If you want to use the Hint syntax in these earlier versions, add the <code>--comments</code> option when starting the client. For example: <code>mysql -h 127.0.0.1 -P 4000 -uroot --comments</code>.</p><h3 id="hints-do-not-take-effect-because-the-database-name-is-not-specified" style="position:relative"><a href="#hints-do-not-take-effect-because-the-database-name-is-not-specified" aria-label="hints do not take effect because the database name is not specified permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints do not take effect because the database name is not specified</h3><p>If you do not specify the database name when creating a connection, hints might not take effect. For example:</p><p>When connecting to TiDB, you use the <code>mysql -h127.0.0.1 -P4000 -uroot</code> command without the <code>-D</code> option, and then execute the following SQL statements:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ use_index(t, a) */</span> a <span class="hljs-keyword">FROM</span> test.t; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>Because TiDB cannot identify the database for table <code>t</code>, the <code>use_index(t, a)</code> hint does not take effect.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> use_index(.t, a) <span class="hljs-keyword">is</span> inapplicable, <span class="hljs-keyword">check</span> whether the <span class="hljs-keyword">table</span>(.t) <span class="hljs-keyword">exists</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="hints-do-not-take-effect-because-the-database-name-is-not-explicitly-specified-in-cross-table-queries" style="position:relative"><a href="#hints-do-not-take-effect-because-the-database-name-is-not-explicitly-specified-in-cross-table-queries" aria-label="hints do not take effect because the database name is not explicitly specified in cross table queries permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints do not take effect because the database name is not explicitly specified in cross-table queries</h3><p>When executing cross-table queries, you need to explicitly specify database names. Otherwise, hints might not take effect. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">USE test1; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1(a <span class="hljs-type">INT</span>, KEY(a)); USE test2; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2(a <span class="hljs-type">INT</span>, KEY(a)); <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ use_index(t1, a) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> test1.t1, t2; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In the preceding statements, because table <code>t1</code> is not in the current <code>test2</code> database, the <code>use_index(t1, a)</code> hint does not take effect.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> use_index(test2.t1, a) <span class="hljs-keyword">is</span> inapplicable, <span class="hljs-keyword">check</span> whether the <span class="hljs-keyword">table</span>(test2.t1) <span class="hljs-keyword">exists</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In this case, you need to specify the database name explicitly by using <code>use_index(test1.t1, a)</code> instead of <code>use_index(t1, a)</code>.</p><h3 id="hints-do-not-take-effect-because-they-are-placed-in-wrong-locations" style="position:relative"><a href="#hints-do-not-take-effect-because-they-are-placed-in-wrong-locations" aria-label="hints do not take effect because they are placed in wrong locations permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Hints do not take effect because they are placed in wrong locations</h3><p>Hints cannot take effect if they are not placed directly after the specific keywords. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-comment">/*+ use_index(t, a) */</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The warning is as follows:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1064</span> <span class="hljs-operator">|</span> You have an error <span class="hljs-keyword">in</span> your <span class="hljs-keyword">SQL</span> syntax; <span class="hljs-keyword">check</span> the manual that corresponds <span class="hljs-keyword">to</span> your TiDB version <span class="hljs-keyword">for</span> the <span class="hljs-keyword">right</span> syntax <span class="hljs-keyword">to</span> use [parser:<span class="hljs-number">8066</span>]Optimizer hint can <span class="hljs-keyword">only</span> be followed <span class="hljs-keyword">by</span> certain keywords <span class="hljs-keyword">like</span> <span class="hljs-keyword">SELECT</span>, <span class="hljs-keyword">INSERT</span>, etc. <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In this case, you need to place the hint directly after the <code>SELECT</code> keyword. For more details, see the <a href="#syntax">Syntax</a> section.</p><h3 id="inl_join-hint-does-not-take-effect" style="position:relative"><a href="#inl_join-hint-does-not-take-effect" aria-label="inl_join hint does not take effect permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a><code>INL_JOIN</code> hint does not take effect</h3><h4 id="inl_join-hint-does-not-take-effect-when-built-in-functions-are-used-on-columns-for-joining-tables" style="position:relative"><a href="#inl_join-hint-does-not-take-effect-when-built-in-functions-are-used-on-columns-for-joining-tables" aria-label="inl_join hint does not take effect when built in functions are used on columns for joining tables permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a><code>INL_JOIN</code> hint does not take effect when built-in functions are used on columns for joining tables</h4><p>In some cases, if you use a built-in function on a column that joins tables, the optimizer might fail to choose the <code>IndexJoin</code> plan, resulting in the <code>INL_JOIN</code> hint not taking effect either.</p><p>For example, the following query uses the built-in function <code>substr</code> on the column <code>tname</code> that joins tables:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (id <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>) <span class="hljs-keyword">primary</span> key, tname <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>)); <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (id <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>) <span class="hljs-keyword">primary</span> key, tname <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id<span class="hljs-operator">=</span>t2.id <span class="hljs-keyword">and</span> SUBSTR(t1.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>)<span class="hljs-operator">=</span>SUBSTR(t2.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The execution plan is as follows:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_12 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.id, test.t2.id) eq(<span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span>, <span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span>)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─Projection_17(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t2.id, test.t2.tname, substr(test.t2.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_19 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_18 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_18 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_14(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.tname, substr(test.t1.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_16 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_15 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableFullScan_15 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-number">7</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span>, <span class="hljs-number">1</span> warning (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+---------+------+------------------------------------------------------------------------------------+ | Level | Code | Message | +---------+------+------------------------------------------------------------------------------------+ | Warning | 1815 | Optimizer Hint /*+ INL_JOIN(t1, t2) */ or /*+ TIDB_INLJ(t1, t2) */ is inapplicable | +---------+------+------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>As you can see from the preceding example, the <code>INL_JOIN</code> hint does not take effect. This is due to a limitation of the optimizer that prevents using the <code>Projection</code> or <code>Selection</code> operator as the probe side of <code>IndexJoin</code>.</p><p>Starting from TiDB v8.0.0, you can avoid this issue by setting <a href="/tidb/stable/system-variables#tidb_enable_inl_join_inner_multi_pattern-new-in-v700"><code>tidb_enable_inl_join_inner_multi_pattern</code></a> to <code>ON</code>.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> @<span class="hljs-variable">@tidb</span>_enable_inl_join_inner_multi_pattern<span class="hljs-operator">=</span><span class="hljs-keyword">ON</span>; Query OK, <span class="hljs-number">0</span> <span class="hljs-keyword">rows</span> affected (<span class="hljs-number">0.00</span> sec) EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id<span class="hljs-operator">=</span>t2.id <span class="hljs-keyword">AND</span> SUBSTR(t1.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>)<span class="hljs-operator">=</span>SUBSTR(t2.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>); <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_18 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:Projection_14, <span class="hljs-keyword">outer</span> key:test.t1.id, <span class="hljs-keyword">inner</span> key:test.t2.id, equal cond:eq(<span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span>, <span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span>), eq(test.t1.id, test.t2.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─Projection_32(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.tname, substr(test.t1.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_34 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_14(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">100000000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t2.id, test.t2.tname, substr(test.t2.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t2.id, test.t1.id)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">7</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h4 id="inl_join-inl_hash_join-and-inl_merge_join-hints-do-not-take-effect-due-to-collation-incompatibility" style="position:relative"><a href="#inl_join-inl_hash_join-and-inl_merge_join-hints-do-not-take-effect-due-to-collation-incompatibility" aria-label="inl_join inl_hash_join and inl_merge_join hints do not take effect due to collation incompatibility permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a><code>INL_JOIN</code>, <code>INL_HASH_JOIN</code>, and <code>INL_MERGE_JOIN</code> hints do not take effect due to collation incompatibility</h4><p>When the collation of the join key is incompatible between two tables, the <code>IndexJoin</code> operator cannot be utilized to execute the query. In this case, the <a href="#inl_joint1_name--tl_name-"><code>INL_JOIN</code></a>, <a href="#inl_hash_join"><code>INL_HASH_JOIN</code></a>, and <a href="#inl_merge_join"><code>INL_MERGE_JOIN</code></a> hints do not take effect. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (k <span class="hljs-type">varchar</span>(<span class="hljs-number">8</span>), key(k)) <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_general_ci; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (k <span class="hljs-type">varchar</span>(<span class="hljs-number">8</span>), key(k)) <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_bin; EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ tidb_inlj(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.k<span class="hljs-operator">=</span>t2.k; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>The execution plan is as follows:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_19 <span class="hljs-operator">|</span> <span class="hljs-number">12487.50</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.k, test.t2.k)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexReader_24(Build) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_23 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_23 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2, index:k(k) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_22(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:k(k) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-number">5</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span>, <span class="hljs-number">1</span> warning (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In the preceding statements, the collations of <code>t1.k</code> and <code>t2.k</code> are incompatible (<code>utf8mb4_general_ci</code> and <code>utf8mb4_bin</code> respectively), which prevents the <code>INL_JOIN</code> or <code>TIDB_INLJ</code> hint from taking effect.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SHOW</span> WARNINGS; <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> Optimizer Hint <span class="hljs-comment">/*+ INL_JOIN(t1) */</span> <span class="hljs-keyword">or</span> <span class="hljs-comment">/*+ TIDB_INLJ(t1) */</span> <span class="hljs-keyword">is</span> inapplicable <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h4 id="inl_join-hint-does-not-take-effect-due-to-join-order" style="position:relative"><a href="#inl_join-hint-does-not-take-effect-due-to-join-order" aria-label="inl_join hint does not take effect due to join order permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a><code>INL_JOIN</code> hint does not take effect due to join order</h4><p>The <a href="#inl_joint1_name--tl_name-"><code>INL_JOIN(t1, t2)</code></a> or <code>TIDB_INLJ(t1, t2)</code> hint semantically instructs <code>t1</code> and <code>t2</code> to act as inner tables in an <code>IndexJoin</code> operator to join with other tables, rather than directly joining them using an <code>IndexJoin</code> operator. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ inl_join(t1, t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id <span class="hljs-keyword">AND</span> t1.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_16 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_13, <span class="hljs-keyword">outer</span> key:test.t2.id, test.t1.id, <span class="hljs-keyword">inner</span> key:test.t3.id, test.t3.id, equal cond:eq(test.t1.id, test.t3.id), eq(test.t2.id, test.t3.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexJoin_34(Build) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_31, <span class="hljs-keyword">outer</span> key:test.t2.id, <span class="hljs-keyword">inner</span> key:test.t1.id, equal cond:eq(test.t2.id, test.t1.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ ├─TableReader_40(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_39 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ │ └─TableFullScan_39 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_31(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_30 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableRangeScan_30 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t2.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_13(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t3 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t2.id test.t1.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>In the preceding example, <code>t1</code> and <code>t3</code> are not directly joined together by an <code>IndexJoin</code>.</p><p>To perform a direct <code>IndexJoin</code> between <code>t1</code> and <code>t3</code>, you can first use <a href="#leadingt1_name--tl_name-"><code>LEADING(t1, t3)</code> hint</a> to specify the join order of <code>t1</code> and <code>t3</code>, and then use the <code>INL_JOIN</code> hint to specify the join algorithm. For example:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ leading(t1, t3), inl_join(t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id <span class="hljs-keyword">AND</span> t1.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Projection_12 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.name, test.t2.id, test.t2.name, test.t3.id, test.t3.name <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─HashJoin_21 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.id, test.t2.id) eq(test.t3.id, test.t2.id)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_36(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_35 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_35 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexJoin_28(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_25, <span class="hljs-keyword">outer</span> key:test.t1.id, <span class="hljs-keyword">inner</span> key:test.t3.id, equal cond:eq(test.t1.id, test.t3.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_34(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_25(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_24 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_24 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t3 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t1.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">9</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="using-hints-causes-the-cant-find-a-proper-physical-plan-for-this-query-error" style="position:relative"><a href="#using-hints-causes-the-cant-find-a-proper-physical-plan-for-this-query-error" aria-label="using hints causes the cant find a proper physical plan for this query error permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Using hints causes the <code>Can't find a proper physical plan for this query</code> error</h3><p>The <code>Can't find a proper physical plan for this query</code> error might occur in the following scenarios:</p><ul><li>A query itself does not require reading indexes in order. That is, for this query, the optimizer does not generate a plan to read indexes in order in any case without using hints. In this case, if the <code>ORDER_INDEX</code> hint is specified, this error occurs. To resolve this issue, remove the corresponding <code>ORDER_INDEX</code> hint.</li><li>A query excludes all possible join methods by using the <code>NO_JOIN</code> related hints.</li></ul><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (a <span class="hljs-type">INT</span>); <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (a <span class="hljs-type">INT</span>); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_HASH_JOIN(t1), NO_MERGE_JOIN(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a<span class="hljs-operator">=</span>t2.a; ERROR <span class="hljs-number">1815</span> (HY000): Internal : Can<span class="hljs-string">'t find a proper physical plan for this query