Question

I want to use CASE in WHERE clause, but it returns error.

Can I use CASE in where clause? or how to fix it ? Thanks

SELECT * FROM hris_leave.dbo.tbl_act 
inner join hris_leave.dbo.tstaff on hris_leave.dbo.tstaff.s_id =        hris_leave.dbo.tbl_act.s_id 
where 
 case when acting_to is not null 
then 
datediff(day, acting_from, acting_to) >= 90 and acting_to >= '2010-10-01' 
else
acting_to is null
order by  hris_leave.dbo.tbl_act.s_id 

Answer 1

In your case, you only need OR

WHERE
    (
    acting_to is null 
    OR 
        (
        datediff(day, acting_from, acting_to) >= 90
        AND
        acting_to >= '2010-10-01'
        )
    )

A case is for values, not conditions. The condition is outside the CASE expression

eg

CASE
    WHEN SomeCol = 'a' THEN ColA
    WHEN SomeCol = 'c' THEN ColC
    ELSE ColB
END > 42