Question

I want to use case statement in where clause but getting error in the query below.

where 
 (r.WeekId=@WeekId or @WeekId is null) and
 (ShiftId=@ShiftId or @ShiftId is null)
 and (placeid=@PlaceId or @PlaceId is null)
 and (r.StatusId=3)
 AND     
CASE WHEN @day = 1 THEN ((firstday=@time and (allocateddays is null or NOT (AllocatedDays  LIKE '%1%')))) 
 WHEN @day = 2 THEN ((secondday=@time and (allocateddays is null or NOT (AllocatedDays LIKE '%2%'))))  
 WHEN @day = 3 THEN ((thirdday=@time  and (allocateddays is null or NOT (AllocatedDays LIKE '%3%')))) 
 ELSE AND (1 = 1) 
END

I am getting error at Case statement at line CASE WHEN @day = 1. What is going wrong with my query. Please help.

Answer 1

The CASE should be rewritten as an OR chain each of which uses @day = n for one of its conditions, owing to the fact that it CASE is expceted to return a value. It cannot execute conditionally in a WHERE clause.

If the condition like @day = 1 returns TRUE, it is used as a boolean AND with the rest of the statement. Each of these is chained via OR to the previous.

where 
 (r.WeekId=@WeekId or @WeekId is null) and
 (ShiftId=@ShiftId or @ShiftId is null)
 and (placeid=@PlaceId or @PlaceId is null)
 and (r.StatusId=3)
 /* I *think* I have the () groups correct here... There's an unnecessary double (()) around firstday|secondday|thirddad */
 AND (
   (@day = 1 AND ((firstday=@time and (allocateddays is null or NOT (AllocatedDays  LIKE '%1%')))))
   OR (@day = 2 AND ((secondday=@time and (allocateddays is null or NOT (AllocatedDays LIKE '%2%')))))
   OR (@day = 3 AND ((thirdday=@time  and (allocateddays is null or NOT (AllocatedDays LIKE '%3%')))))
   /* Not certain if this is necessary in your case, as a catch-all to replace your ELSE */
   OR (@day NOT IN (1,2,3) AND 1=1) 
 )