Question

Below is a stored procedure to check if there is a duplicate entry in the database based upon checking all the fields individually (don’t ask why I should do this, it just has to be this way).

It sounds perfectly straightforward but the SP fails. The problem is that some parameters passed into the SP may have a null value and therefore the sql should read ‘is null’ rather than ‘= null’. I have tried isnull(),case statements,coalesce() and dynamic sql with exec() and sp_executesql and failed to implement any of these. Here is the code…

CREATE PROCEDURE sp_myDuplicateCheck  @userId int,  @noteType char(1),  @aCode char(3),  @bCode char(3),   @cCode char(3),  @outDuplicateFound int OUT AS BEGIN SET @outDuplicateFound = (SELECT Top 1 id FROM codeTable                            WHERE userId = @userId                           AND noteType = @noteType                           AND aCode = @aCode                           AND bCode = @bCode                           AND cCode = @cCode                            ) -- Now set the duplicate output flag to a 1 or a 0 IF (@outDuplicateFound IS NULL) OR (@outDuplicateFound = '') OR (@outDuplicateFound = 0)  SET @outDuplicateFound = 0 ELSE   SET @outDuplicateFound = 1 END 

Answer 1

I think you need something like this for each possibly-null parameter:

AND (aCode = @aCode OR (aCode IS NULL AND @aCode IS NULL))