SQL Case语句以确定过滤器

Question

I am having this issue here. I am trying to use a case statement to determine which filter to use. It is OK to use it for single values, but it is not OK to use a Select Statement results.

DECLARE @SingleValue INT = 0

SELECT 
    t1.Field1
    , t1.Field2
    , t1.Field3
FROM 
    tblTable1 t1
    INNER JOIN tblTable2 t2 ON t1.Field1 = t2.Field
WHERE 
    t1.Field2 IN (SELECT CASE WHEN @SingleValue = 0 THEN (SELECT Field1 FROM tblTable3) ELSE t1.Field2 END)
    AND t2.Field2 = (CASE WHEN @SingleValue = 0 THEN t2.Field2 ELSE @SingleValue END)

Once the @singleValue is set to a value '123' then it is working fine, the moment when I set the value to '0' (ZERO) then it returns an error 'Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.'

The problem start with '(SELECT Field1 FROM tblTable3)' in the case statement. How can I work around it to get multiple values in the case statement.

Thanks.

Answer 1

Maybe something like:

DECLARE @SingleValue INT = 0

SELECT 
    t1.Field1
    , t1.Field2
    , t1.Field3
FROM 
    tblTable1 t1
    INNER JOIN tblTable2 t2 ON t1.Field1 = t2.Field
WHERE 
    (
        ( @SingleValue <> 0 )
        or
        ( t1.Field2 IN ( SELECT Field1 FROM tblTable3) )
    )
    and
    (
        ( @SingleValue = 0 )
        or
        ( t2.Field2 = @SingleValue )
    )