Question

I’m trying to add a case or if statement in the where clause of my SQL query.
I have a table of journey times with a start and end date, and a boolean field for each day to signify where the journey happens on that day. Here is what I have so far, but I’m getting incorrect syntax errors:

declare @date datetime
set @Date = '05/04/2012' 
declare @day nvarchar(50)
set @day = 'Monday'

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date)
CASE WHEN @day = 'Monday' THEN
 AND (Monday = 1)
WHEN @day = 'Tuesday' THEN
AND (Tuesday = 1)
ELSE
AND (Wednesday = 1) 
END 

Answer 1

You don’t need case in the where statement, just use parentheses and or:

Select * From Times
WHERE StartDate <= @Date AND EndDate >= @Date
AND (
    (@day = 'Monday' AND Monday = 1)
    OR (@day = 'Tuesday' AND Tuesday = 1)
    OR Wednesday = 1
)

Additionally, your syntax is wrong for a case. It doesn’t append things to the string–it returns a single value. You’d want something like this, if you were actually going to use a case statement (which you shouldn’t):

Select * From Times
WHERE (StartDate <= @Date) AND (EndDate >= @Date)
AND 1 = CASE WHEN @day = 'Monday' THEN Monday
             WHEN @day = 'Tuesday' THEN Tuesday
             ELSE Wednesday
        END 

And just for an extra umph, you can use the between operator for your date:

where @Date between StartDate and EndDate

Making your final query:

select
    * 
from 
    Times
where
    @Date between StartDate and EndDate
    and (
        (@day = 'Monday' and Monday = 1)
        or (@day = 'Tuesday' and Tuesday = 1)
        or Wednesday = 1
    )