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I am working with a query which contains "CASE" statement within "WHERE" clause. But SQL Server 2008 is giving some errors while executing it. Can anyone please help me with the correct query? Here is the query:

SELECT
    tl.storenum 'Store #', 
    co.ccnum 'FuelFirst Card #', 
    co.dtentered 'Date Entered',
    CASE st.reasonid 
        WHEN 1 THEN 'Active' 
   WHEN 2 THEN 'Not Active' 
   WHEN 0 THEN st.ccstatustypename 
   ELSE 'Unknown' 
    END 'Status',
    CASE st.ccstatustypename 
        WHEN 'Active' THEN ' ' 
   WHEN 'Not Active' THEN ' ' 
   ELSE st.ccstatustypename 
    END 'Reason',
    UPPER(REPLACE(REPLACE(co.personentered,'RT\\\\',''),'RACETRAC\\\\','')) 'Person Entered',
    co.comments 'Comments or Notes'
    comments co
    INNER JOIN cards cc ON co.ccnum=cc.ccnum
    INNER JOIN customerinfo ci ON cc.customerinfoid=ci.customerinfoid
    INNER JOIN ccstatustype st ON st.ccstatustypeid=cc.ccstatustypeid
    INNER JOIN customerstatus cs ON cs.customerstatuscd=ci.customerstatuscd
    INNER JOIN transactionlog tl ON tl.transactionlogid=co.transactionlogid
    LEFT JOIN stores s ON s.StoreNum = tl.StoreNum
WHERE 
    CASE LEN('TestPerson')
        WHEN 0 THEN co.personentered  = co.personentered
   ELSE co.personentered LIKE '%TestPerson'
    AND cc.ccnum = CASE LEN('TestFFNum')
        WHEN 0 THEN cc.ccnum 
   ELSE 'TestFFNum' 
    AND CASE LEN('2011-01-09 11:56:29.327') 
        WHEN 0 THEN co.DTEntered = co.DTEntered 
       CASE LEN('2012-01-09 11:56:29.327') 
           WHEN 0 THEN co.DTEntered >= '2011-01-09 11:56:29.327' 
      ELSE co.DTEntered BETWEEN '2011-01-09 11:56:29.327' AND '2012-01-09 11:56:29.327' 
    AND tl.storenum < 699 
ORDER BY tl.StoreNum
                Case expression, not statement... (The case expression returns a value. The case statement is used in stored procedures for conditional execution of code.)
– jarlh
                Sep 11, 2018 at 12:20
First off, the CASE statement must be part of the expression, not the expression itself. 
In other words, you can have:
WHERE co.DTEntered = CASE 
                          WHEN LEN('blah') = 0 
                               THEN co.DTEntered 
                          ELSE '2011-01-01' 
But it won't work the way you have written them eg:
WHERE 
    CASE LEN('TestPerson')
        WHEN 0 THEN co.personentered  = co.personentered
   ELSE co.personentered LIKE '%TestPerson'
You may have better luck using combined OR statements like this:
WHERE (
        (LEN('TestPerson') = 0 
             AND co.personentered = co.personentered
        (LEN('TestPerson') <> 0 
             AND co.personentered LIKE '%TestPerson')
Although, either way I'm not sure how great of a query plan you'll get. These types of shenanigans in a WHERE clause will often prevent the query optimizer from utilizing indexes. 
                WHEN 0 THEN co.personentered  = co.personentered, Here this check co.personentered  = co.personentered is not needed as it will always return true and length value will always be positive. So, making LEN('TestPerson') > 0 will reduce the range needed to be compared
– Satyajit
                Nov 10, 2014 at 8:30
                how to check co.personentered is not null, in option 1 and 2. Now 3 rd option is enough. But I want to know that...!!
– Pugal
                Mar 1, 2019 at 15:18
                i tried so far where  case c  when 1 then (DescriptionCode is null)   else descriptioncode is not null  end, but i shows the error like Incorrect syntax near the keyword 'is'.
– Pugal
                Mar 1, 2019 at 15:23
This should solve your problem for the time being but I must remind you it isn't a good approach :
WHERE 
            CASE LEN('TestPerson')
                WHEN 0 THEN 
                        CASE WHEN co.personentered  = co.personentered THEN 1 ELSE 0 END
                        CASE WHEN co.personentered LIKE '%TestPerson' THEN 1 ELSE 0 END
            END = 1
        AND cc.ccnum = CASE LEN('TestFFNum')
                            WHEN 0 THEN cc.ccnum 
                            ELSE 'TestFFNum' 
        AND CASE LEN('2011-01-09 11:56:29.327') 
                WHEN 0 THEN CASE WHEN co.DTEntered = co.DTEntered THEN 1 ELSE 0 END 
                    CASE LEN('2012-01-09 11:56:29.327') 
                        WHEN 0 THEN 
                            CASE WHEN co.DTEntered >= '2011-01-09 11:56:29.327' THEN 1 ELSE 0 END 
                            CASE WHEN co.DTEntered BETWEEN '2011-01-09 11:56:29.327' 
                                                        AND '2012-01-09 11:56:29.327' 
                                                     THEN 1 ELSE 0 END
            END = 1
        AND tl.storenum < 699 
        ELSE st.ccstatustypename 
        END [Reason],
    UPPER(REPLACE(REPLACE(co.personentered,'RT\\\\',''),'RACETRAC\\\\','')) [Person Entered],
    co.comments [Comments or Notes]
FROM comments co
    INNER JOIN cards cc ON co.ccnum=cc.ccnum
    INNER JOIN customerinfo ci ON cc.customerinfoid=ci.customerinfoid
    INNER JOIN ccstatustype st ON st.ccstatustypeid=cc.ccstatustypeid
    INNER JOIN customerstatus cs ON cs.customerstatuscd=ci.customerstatuscd
    INNER JOIN transactionlog tl ON tl.transactionlogid=co.transactionlogid
    LEFT JOIN stores s ON s.StoreNum = tl.StoreNum
WHERE 
      WHEN (LEN([TestPerson]) = 0 AND co.personentered  = co.personentered) OR (LEN([TestPerson]) <> 0 AND co.personentered LIKE '%'+TestPerson) THEN 1
      ELSE 0
      END = 1
what is in the tail is completely not understandable
WHERE 
 (LEN('TestPerson') <> 0 OR co.personentered  = co.personentered) AND
 (LEN('TestPerson') = 0 OR co.personentered LIKE '%TestPerson') AND
 (cc.ccnum = CASE LEN('TestFFNum')
                WHEN 0 THEN cc.ccnum 
                ELSE 'TestFFNum' 
              END ) AND
 (LEN('2011-01-09 11:56:29.327') <> 0 OR co.DTEntered = co.DTEntered ) AND
 ((LEN('2011-01-09 11:56:29.327') = 0 AND LEN('2012-01-09 11:56:29.327') <> 0) OR co.DTEntered >= '2011-01-09 11:56:29.327'  ) AND
 ((LEN('2011-01-09 11:56:29.327') = 0 AND LEN('2012-01-09 11:56:29.327') = 0) OR co.DTEntered BETWEEN '2011-01-09 11:56:29.327' AND '2012-01-09 11:56:29.327'  ) AND 
 tl.storenum < 699 
d.DISTNAME,e.BLKNAME,a.childid,a.studyingclass 
from Tbl_AdmissionRegister a
inner join District_master b on a.Schooid=b.Schooid
where 
case when len('3601')=4   then c.distcd 
           when len('3601')=6   then c.blkcd  
           when len('3601')=11  then c.schcd   end = '3601'
                Please provide more information as to why your answer helps solve the original question. Posting just code can be a little vague for users with the same problem.
– Harry J
                Sep 25, 2020 at 13:42
Thanks for this question, actually I am looking for something else which is in below query. this may helps someone. 
      SELECT DISTINCT CASE WHEN OPPORTUNITY='' THEN '(BLANK)' ELSE OPPORTUNITY END
  AS OPP,LEN(OPPORTUNITY) FROM [DBO].[TBL]
above query is to fill in dropdown which blank values shows as "(blank)". Also if we pass this value into sql where clause to get blank values with other values I don't know how to handle that. And finally came up with below solution this may helps to somebody.
here it is ,
 DECLARE @OPP TABLE (OPP VARCHAR(100))
  INSERT INTO @OPP VALUES('(BLANK)'),('UNFUNDED'),('FUNDED/NOT COMMITTED')
SELECT DISTINCT [OPPORTUNITY]
FROM [DBO].[TBL]   WHERE    (  CASE WHEN   OPPORTUNITY ='' THEN '(BLANK)' ELSE OPPORTUNITY END IN (SELECT OPP FROM @OPP))
ORDER BY 1 
You could also try like below eg. to show only Outbound Shipments
   SELECT shp_awb_no,shpr_ctry_cd, recvr_ctry_cd,
     CASE WHEN shpr_ctry_cd = record_ctry_cd 
     THEN "O" 
     ELSE "I" 
      END AS route
     FROM shipment_details
    WHERE record_ctry_cd = "JP"
      AND "O" = CASE WHEN shpr_ctry_cd = record_ctry_cd 
                THEN "O" 
                ELSE "I" 
CASE LEN('TestPerson')
    WHEN 0 THEN co.personentered  = co.personentered ELSE co.personentered LIKE '%TestPerson'
Try the following:
... and ( 
    (LEN('TestPerson') = 0 and co.personentered  = co.personentered) or
    (LEN('TestPerson') <> 0 and co.personentered LIKE '%TestPerson') ) and ...
I'm using somtehing like that to filter users according to needle as string and a dropdown in the UI
where 
        u.username like '%' + isnull(@needle, '') + '%'
    and 1 =
            when @status = 0            then 1 -- All in uu
            when @status = u.statusid   then 1 -- Special status 
            else 0 -- otherwise reject
select TUM1.userid,TUM1.first_name + ' ' +TUM1.last_name as NAME,tum1.Business_Title,TUM1.manager_id,tum2.First_Name + ' ' + tum2.Last_Name as [MANAGER NAME],TUM1.project,TUM1.project_code,TUM1.rcc_code,TUM1.department,TCM.Company_Name,
when tum1.Gender_ID=1 then 'male' 
else 'female' 
end 'GENDER'
,tum1.Band as BAND,
case when tum1.Inactive=0 then 'STILL IN COMPANY'
else 'LEFT COMPANY' 
end 'ACTIVE/INACTIVE'
from tbl_user_master TUM1
join tbl_Company_Master TCM on TCM.Company_Code=TUM1.Company_Code 
join tbl_User_Master TUM2 on TUM1.Manager_ID=TUM2.UserID 
where tum1.UserID in ('54545414')
SELECT * from TABLE 
              WHERE 1 = CASE when TABLE.col = 100 then 1 
                     when TABLE.col = 200 then 2 else 3 END 
                  and TABLE.col2 = 'myname';
Use in this way.
        
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