SQL Case NOT NULL as value

Question

I'm trying to return NOT NULL and NULL as the result of a CASE statement but I can't find the right way to do it

What I have below is incorrect and underlines the NOT keyword

SELECT  ROW_NUMBER() OVER ( ORDER BY d.cnumber DESC) AS RowNum,
    d.cnumber,
    d.firstname,
    d.lastname,
    d.current_email,
    d.updated_email,
    d.optedin,
    d.activated             
FROM    
    Customer d 
WHERE (d.optedin = 
           CASE WHEN @query = 'UNSUBMITTED' OR @query = 'SUBMITTED' 
                    THEN d.optedin
                WHEN @query = 'OPTEDIN' 
                    THEN 1
                ELSE 0 END) AND
      (d.activated =
           CASE WHEN @query = 'OPTEDIN' OR @query = 'OPTEDOUT' 
                    THEN d.activated 
                WHEN @query = 'UNSUBMITTED' 
                    THEN NULL 
                ELSE NOT NULL END)

activated is a nullable datetime field. @query is a varchar parameter

Answer 1

Using a case in a where clause is usually an indication you've taken the wrong path. I believe that you'll find you can solve this with more standard logic:

WHERE (@query in ( 'UNSUBMITTED', 'SUBMITTED') 
         OR (@query = 'OPTEDIN' AND d.optedin = 1)
         OR d.optedin = 0)
       AND
      (@query in ('OPTEDIN', 'OPTEDOUT')
         OR (@query = 'UNSUBMITTED' AND d.activated IS NULL)
         OR  d.activated IS NOT NULL)

Answer 2

I suggest you modify the condition for d.activated to this:

AND (@query = 'UNSUBMITTED' AND d.activated IS NULL OR @query <> 'UNSUBMITTED' AND d.activated IS NOT NULL)

Please note that you do not need to specifically test for this condition:

CASE WHEN @query = 'OPTEDIN' OR @query = 'OPTEDOUT' 
                THEN d.activated 

As it will be covered by OR d.activated IS NOT NULL in the condition that I have proposed

BTW, for d.optedin you can use the similar:

(@query = 'OPTEDIN' AND d.optedin = 1 OR @query <> 'OPTEDIN' AND d.optedin = 0)

Answer 3

This:

ELSE NOT NULL 

is too vague. SQL Server does not know what to return. You have to specify a value that is the same datatype as d.activated.