Posted by Ed Murphy on 01/25/08 06:48

Jared wrote:

> Consider the following two functionally identical example queries:
>
> Query 1:
>
> DECLARE @Name VARCHAR(32)
> SET @Name = 'Bob'
> SELECT * FROM Employees
> WHERE [Name] = CASE WHEN @Name IS NULL THEN [Name] ELSE @Name END
>
> Query 2:
>
> SELECT * FROM Employees WHERE [Name] = 'Bob'
>
> I would expect SQL Server to construct an identical QEP under the hood
> for these two queries, and that they would require essentially the
> same amount of time to execute. However, Query 1 takes much longer to
> run on my indexed table of ~300,000 rows. By "longer", I mean that
> Query 1 takes about two seconds, while Query 2 returns almost
> instantly.
>
> Is there a way to implement a conditional WHERE clause without
> suffering this performance hit? I want to avoid using the IF...THEN
> method because I frequently require several optional parameters in the
> WHERE clause.

I would at least try the following:

WHERE (@Name IS NULL OR [Name] = @Name)

as well as

WHERE NOT([Name] <> @Name)

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