Alternative to SET ANSI_NULLS OFF in a WHERE clause

Question

I have a SP that has a very complex SQL statement(s) where I need to be able to compare some column to NULL eg

...
FROM Categories
WHERE PID = @parentID

@parentID is a SP parameter which can be valid NULL.
PID (parent ID) is uniqueidentifier which can also be valid NULL (top level category). I could use SET ANSI_NULLS OFF but the documentation says:

In a future version of SQL Server, ANSI_NULLS will always be ON and any applications that explicitly set the option to OFF will generate an error. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.

What can be an elegant way instead of repeating the same query(s) with IS NULL in case @parentID=NULL (and also not using dynamic SQL):

IF @parentID IS NULL 
  SELECT...WHERE PID IS NULL
ELSE
  SELECT...WHERE PID = @parentID

EDIT: I want to avoid an IF because I hate repeating (huge) code.

Answer 1

Something like:

select ..
FROM Categories
WHERE PID = @parentID or (PID is null and @parentID is null)

Answer 2

I think the if version is the clearest. A big issue with multiple queries, though, is that the stored procedure compiles the code when it is first run -- and it might make the wrong decision about the execution plan.

One option is to include recompile .

Another is to combine the queries, but in a way where each part should use indexes effectively:

select c.* from categories c where pid is null and @parentid is null
union all
select c.* from categories c where pid = @parentId;

This is a tiny bit less efficient than the if version.

Answer 3

Here is an elegant and concise way to code this:

SELECT *
FROM Categories
WHERE COALESCE(PID, 'NULL-MATCH') = COALESCE(@parentID, 'NULL-MATCH')