"CASE" statement within "WHERE" clause in SQL Server 2008

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'
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 
    CASE LEN('TestPerson')
        WHEN 0 THEN co.personentered  = co.personentered
   ELSE co.personentered LIKE '%TestPerson'
    END 
    AND cc.ccnum = CASE LEN('TestFFNum')
        WHEN 0 THEN cc.ccnum 
   ELSE 'TestFFNum' 
    END 
    AND CASE LEN('2011-01-09 11:56:29.327') 
        WHEN 0 THEN co.DTEntered = co.DTEntered 
   ELSE 
       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' 
       END 
    END
    AND tl.storenum < 699 
ORDER BY tl.StoreNum

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' 
                     END 

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'
    END 

You may have better luck using combined OR statements like this:

WHERE (
        (LEN('TestPerson') = 0 
             AND co.personentered = co.personentered
        ) 
        OR 
        (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.

Try the following:

SELECT * FROM emp_master 
WHERE emp_last_name= 
CASE emp_first_name 
 WHEN 'test'    THEN 'test' 
 WHEN 'Mr name' THEN 'name'
END

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
                ELSE 
                        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' 
                       END 
        AND CASE LEN('2011-01-09 11:56:29.327') 
                WHEN 0 THEN CASE WHEN co.DTEntered = co.DTEntered THEN 1 ELSE 0 END 
                ELSE 
                    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 
                        ELSE 
                            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
            END = 1
        AND tl.storenum < 699 

I think that the beginning of your query should look like that:

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]
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 
    CASE 
      WHEN (LEN([TestPerson]) = 0 AND co.personentered  = co.personentered) OR (LEN([TestPerson]) <> 0 AND co.personentered LIKE '%'+TestPerson) THEN 1
      ELSE 0
      END = 1
    AND 

BUT

what is in the tail is completely not understandable