The DECLARE ... HANDLER statement specifies a handler that deals with one or more conditions. If one of these conditions occurs, the specified statement executes. statement can be a simple statement such as SET var_name = value , or a compound statement written using BEGIN and END (see Section 13.6.1, “BEGIN ... END Compound Statement” ). Handler declarations must appear after variable or condition declarations. The handler_action value indicates what action the handler takes after execution of the handler statement: CONTINUE : Execution of the current program continues. EXIT : Execution terminates for the BEGIN ... END compound statement in which the handler is declared. This is true even if the condition occurs in an inner block. UNDO : Not supported. The condition_value for DECLARE ... HANDLER indicates the specific condition or class of conditions that activates the handler. It can take the following forms: mysql_error_code : An integer literal indicating a MySQL error code, such as 1051 to specify “ unknown table ” :

DECLARE CONTINUE HANDLER FOR 1051
  BEGIN
    -- body of handler
            Do not use MySQL error code 0 because that indicates success
            rather than an error condition. For a list of MySQL error
            codes, see Server Error Message Reference.
            SQLSTATE [VALUE] sqlstate_value:
            A 5-character string literal indicating an SQLSTATE value,
            such as '42S01' to specify “unknown
            table”:
          
DECLARE CONTINUE HANDLER FOR SQLSTATE '42S02'
  BEGIN
    -- body of handler
            Do not use SQLSTATE values that begin with
            '00' because those indicate success
            rather than an error condition. For a list of SQLSTATE
            values, see Server Error Message Reference.
            condition_name: A condition name
            previously specified with
            DECLARE
            ... CONDITION. A condition name can be associated
            with a MySQL error code or SQLSTATE value. See
            Section 13.6.7.1, “DECLARE ... CONDITION Statement”.
            SQLWARNING: Shorthand for the class of
            SQLSTATE values that begin with '01'.
          
DECLARE CONTINUE HANDLER FOR SQLWARNING
  BEGIN
    -- body of handler
            NOT FOUND: Shorthand for the class of
            SQLSTATE values that begin with '02'.
            This is relevant within the context of cursors and is used
            to control what happens when a cursor reaches the end of a
            data set. If no more rows are available, a No Data condition
            occurs with SQLSTATE value '02000'. To
            detect this condition, you can set up a handler for it or
            for a NOT FOUND condition.
          
DECLARE CONTINUE HANDLER FOR NOT FOUND
  BEGIN
    -- body of handler
            For another example, see Section 13.6.6, “Cursors”. The
            NOT FOUND condition also occurs for
            SELECT ... INTO
            var_list statements
            that retrieve no rows.
            SQLEXCEPTION: Shorthand for the class of
            SQLSTATE values that do not begin with
            '00', '01', or
            '02'.
          
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION
  BEGIN
    -- body of handler
        For information about how the server chooses handlers when a
        condition occurs, see Section 13.6.7.6, “Scope Rules for Handlers”.
        If a condition occurs for which no handler has been declared,
        the action taken depends on the condition class:
            For SQLEXCEPTION conditions, the stored
            program terminates at the statement that raised the
            condition, as if there were an EXIT
            handler. If the program was called by another stored
            program, the calling program handles the condition using the
            handler selection rules applied to its own handlers.
            For SQLWARNING conditions, the program
            continues executing, as if there were a
            CONTINUE handler.
            For NOT FOUND conditions, if the
            condition was raised normally, the action is
            CONTINUE. If it was raised by
            SIGNAL or
            RESIGNAL, the action is
            EXIT.
        The following example uses a handler for SQLSTATE
        '23000', which occurs for a duplicate-key error:
      
mysql> CREATE TABLE test.t (s1 INT, PRIMARY KEY (s1));
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter //
mysql> CREATE PROCEDURE handlerdemo ()
       BEGIN
         DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1;
         SET @x = 1;
         INSERT INTO test.t VALUES (1);
         SET @x = 2;
         INSERT INTO test.t VALUES (1);
         SET @x = 3;
Query OK, 0 rows affected (0.00 sec)
mysql> CALL handlerdemo()//
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @x//
    +------+
    | @x   |
    +------+
    | 3    |
    +------+
    1 row in set (0.00 sec)

        Notice that @x is 3 after
        the procedure executes, which shows that execution continued to
        the end of the procedure after the error occurred. If the
        DECLARE ...
        HANDLER statement had not been present, MySQL would
        have taken the default action (EXIT) after
        the second INSERT failed due to
        the PRIMARY KEY constraint, and
        SELECT @x would have returned
        To ignore a condition, declare a CONTINUE
        handler for it and associate it with an empty block. For
        example:
      
DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN END;

        The scope of a block label does not include the code for
        handlers declared within the block. Therefore, the statement
        associated with a handler cannot use
        ITERATE or
        LEAVE to refer to labels for
        blocks that enclose the handler declaration. Consider the
        following example, where the
        REPEAT block has a label of
        retry:
      
CREATE PROCEDURE p ()
BEGIN
  DECLARE i INT DEFAULT 3;
  retry:
    REPEAT
      BEGIN
        DECLARE CONTINUE HANDLER FOR SQLWARNING
          BEGIN
            ITERATE retry;    # illegal
        IF i < 0 THEN
          LEAVE retry;        # legal
        END IF;
        SET i = i - 1;
    UNTIL FALSE END REPEAT;
        The retry label is in scope for the
        IF statement within the block. It
        is not in scope for the CONTINUE handler, so
        the reference there is invalid and results in an error:
      
ERROR 1308 (42000): LEAVE with no matching label: retry

        To avoid references to outer labels in handlers, use one of
        these strategies:
            To leave the block, use an EXIT handler.
            If no block cleanup is required, the
            BEGIN ...
            END handler body can be empty:
          
DECLARE EXIT HANDLER FOR SQLWARNING BEGIN END;

            Otherwise, put the cleanup statements in the handler body:
          
DECLARE EXIT HANDLER FOR SQLWARNING
  BEGIN
    block cleanup statements
            To continue execution, set a status variable in a
            CONTINUE handler that can be checked in
            the enclosing block to determine whether the handler was
            invoked. The following example uses the variable
            done for this purpose:
          
CREATE PROCEDURE p ()
BEGIN
  DECLARE i INT DEFAULT 3;
  DECLARE done INT DEFAULT FALSE;
  retry:
    REPEAT
      BEGIN
        DECLARE CONTINUE HANDLER FOR SQLWARNING
          BEGIN
            SET done = TRUE;
        IF done OR i < 0 THEN
          LEAVE retry;
        END IF;
        SET i = i - 1;
    UNTIL FALSE END REPEAT;