Question

I need to create a query which looks like this:

SELECT attr
FROM SomeTable B
WHERE EXISTS
   
(CASE WHEN B.some_attr = 0

       
THEN (SELECT x FROM C WHERE B.z = z)
    
WHEN B.some_attr = 1
       
THEN (SELECT x FROM D WHERE B.z = x)
    
END)

But SQL Server refuses to execute this bringing some syntax error.
How can I modify this query to make it work?

EDIT: I’m adding the error:

Msg 156, Level 15, State 1, Line 4 Incorrect syntax near the keyword ‘CASE’.
Msg 156, Level 15, State 1, Line 6 Incorrect syntax near the keyword ‘WHEN’.
Msg 102, Level 15, State 1, Line 8 Incorrect syntax near ‘)’.

Answer 1

Try this:

SELECT A 
FROM B 
WHERE 
     CASE 
     WHEN B.some_attr = 0 AND EXISTS(SELECT x FROM C WHERE B.z = z) THEN 1
     WHEN B.some_attr = 1 AND EXISTS(SELECT x FROM D WHERE B.z = x) THEN 1
     END = 1