How to Correctly Use CASE Statements in SQL Server 2008 WHERE Clauses?
Jan 11, 2025 am 10:24 AMSQL Server 2008 WHERE Clause: Proper CASE Statement Usage
Employing CASE statements within SQL Server 2008 WHERE clauses demands precise syntax for correct execution. The following illustrates common errors and their solutions.
An example of incorrect CASE statement placement in a WHERE clause:
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
The problem is the attempt to assign values within the CASE statement using =
or LIKE
. The CASE statement should be used for conditional value generation, not assignment. The corrected approach uses Boolean logic:
WHERE (LEN('TestPerson') = 0 AND co.personentered = co.personentered) OR (LEN('TestPerson') > 0 AND co.personentered LIKE '%TestPerson')
This revised query correctly evaluates the conditions based on the length of 'TestPerson'.
Date comparisons also require careful consideration. Instead of multiple nested CASE statements, using separate OR conditions is often clearer and more efficient:
WHERE (LEN('2011-01-09 11:56:29.327') = 0 AND co.DTEntered = co.DTEntered) OR (LEN('2011-01-09 11:56:29.327') > 0 AND LEN('2012-01-09 11:56:29.327') = 0 AND co.DTEntered >= '2011-01-09 11:56:29.327') OR (LEN('2011-01-09 11:56:29.327') > 0 AND LEN('2012-01-09 11:56:29.327') > 0 AND co.DTEntered BETWEEN '2011-01-09 11:56:29.327' AND '2012-01-09 11:56:29.327')
By employing these corrected syntaxes, your SQL Server 2008 queries incorporating CASE statements within WHERE clauses will execute as intended.
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