T-SQL Stored Procedure NULL input values cause select statement to fail - sql

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))

Answer 2

If I understand your question correctly, then I encourage you to do a little research on:
SET ANSI_NULLS OFF
If you use this command in your stored procedure, then you can use = NULL in your comparison. Take a look at the following example code to see how this works.
Declare #Temp Table(Data Int)
Insert Into #Temp Values(1)
Insert Into #Temp Values(NULL)
-- No rows from the following query
select * From #Temp Where Data = NULL
SET ANSI_NULLS OFF
-- This returns the rows where data is null
select * From #Temp Where Data = NULL
SET ANSI_NULLS ON
Whenever you SET ANSI_NULLS Off, it's a good practice to set it back to ON as soon as possible because this may affect other queries that you run later. All of the SET commands only affect the current session, but depending on your application, this could span multiple queries, which is why I suggest you turn ansi nulls back on immediately after this query.

Answer 3

I think this should work with COALESCE function. Try this:
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 COALESCE(aCode,'NUL') = COALESCE(#aCode,'NUL')
AND COALESCE(bCode,'NUL') = COALESCE(#bCode,'NUL')
AND COALESCE(cCode,'NUL') = COALESCE(#cCode,'NUL')
)
-- 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
Good Luck!
Jason

Answer 4

Try this :
CREATE PROCEDURE sp_myDuplicateCheck
#userId int = 0,
#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 in (userId ,0)
AND #noteType in (noteType,"")
AND #aCode in (aCode , "")
AND #bCode in (bCode , "")
AND #cCode in (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
What this basically does is to provide default values to the input parameters in case of null and then in the where condition checks only if the values are not equal to the default values.

Answer 5

I would first add a check to see if all of the parameters were null at run time, i.e.,
IF(COALESCE(#userId, #noteType, #aCode, #bCode, #cCode) IS NULL)
BEGIN
-- do something here, log, print, return, etc.
END
Then after you've validated that the user passed something in you can use something like this in your WHERE clause
WHERE userId = COALESCE(#userId, userId)
AND noteType = COALESCE(#noteType, noteType)
AND aCode = COALESCE(#aCode, aCode)
AND bCode = COALESCE(#bCode, bCode)
AND cCode = COALESCE(#cCode, cCode)
EDIT: I may have missed the intent that if the parameter was passed in as null that means you explicitly want to test the column for null. My above where clause assumed that the null parameter meant 'skip the test on this column.'
Alternatively, I believe you can use your original query and add the ANSI_NULLS set option at the stored procedure create time. For example,
SET ANSI_NULLS OFF
GO
CREATE PROC sp_myDuplicateCheck....
Effectively this should allow your code to then evaluate column=null as opposed to column is null. I think Kalen Delaney once coined the ANSI_NULLS and QUOTED_IDENTIFIER options as 'sticky options' because if they're set at procedure create time they stay with the procedure at run time, regardless of how the connection at that time is set.

Answer 6

SET ANSI_NULLS OFF/On
That way you can do colName = null