Question

I am trying to get some data from a table and possibly filtering it depending on the result from another query.

The code is something like this:

DECLARE @TestTable  TABLE(TestID INT)

INSERT INTO @TestTable
SELECT TestID from v_Lookuptable Where SomeID = @input


SELECT DISTINCT
C.[Level],
C.Name
FROM
dbo.CPackage CP 
Right outer join @TestTable TT on TT.TestID = CP.TestID
WHERE
AND (TT.TestID is null OR Exists( Select TT.TestID from @TestTable 
                                    inner join dbo.CProduct CP on CP.TestID = MT.TestID
                                    where TT.TestID = CP.TestID
                                    ))

My problem is that if I pass in my currently scenario the @input as 1, then the top part returns some numbers: 1, 2, 3

But if I pass @input as 2, then the top part returns nothing because nothing matches.

The idea is that if nothing matches, return everything in the bottom query, so from dbo.CPackage, else, only return those things where the TestID match.

I have tried various things like changing the joins, case statements, using ISNULL and collasce. Also I have tried to remove the part TT.TestID is null and it then works if the top table returns something, but when I add it again it returns everything and never filters. So I know the logic is wrong… I just can’t figure out the correct logic for this…. :S

Is it possible? I presume it is…

Cheers
Robin

** Solution **

Remove the join and just put it in the where filter…

SELECT DISTINCT
C.[Level],
C.Name
FROM
dbo.CPackage CP 

WHERE
CP.TestID = coalesce( (select distinct TestID from v_Lookuptable LT
        where LT.SomeID =  @input), CP.TestID )

Answer 1

Does this give you what you’re looking for:

SELECT DISTINCT
       CP.[Level]
      ,CP.Name
  FROM dbo.CPackage CP
  LEFT OUTER JOIN @TestTable TT
          ON TT.TestID = CP.TestID
 WHERE CP.TestID = ISNULL(TT.TestID, CP.TestID);

Or, you may even be able to rewrite the entire query like this:

DECLARE @input1 int;
SET @input1 = ...;

-- If there are no records returned for v_Lookuptable, then return all records from CPackage.
-- Otherwise, only return records from CPackage that have a match in the v_Lookuptable where v_Lookuptable.SomeID = @input1.
SELECT DISTINCT
       CP.[Level]
      ,CP.Name
  FROM dbo.CPackage CP
  LEFT OUTER JOIN v_Lookuptable TT
          ON TT.TestID = CP.TestID
         AND SomeID = @input1 --<== Only include records from TT that match @input1...
 WHERE CP.TestID = ISNULL(TT.TestID, CP.TestID); --<== Return all records from CP if TT is NULL.