Is this query equivalent to SQL Server 2008's OPTIMIZE FOR UNKNOWN?

Question

I'm maintaining stored procedures for SQL Server 2005 and I wish I could use a new feature in 2008 that allows the query hint: "OPTIMIZE FOR UNKNOWN"

It seems as though the following query (written for SQL Server 2005) estimates the same number of rows (i.e. selectivity) as if OPTION (OPTIMIZE FOR UNKNOWN) were specified:

CREATE PROCEDURE SwartTest(@productid INT)
AS  
DECLARE @newproductid INT
SET @newproductid = @productid

SELECT ProductID 
FROM Sales.SalesOrderDetail 
WHERE ProductID = @newproductid

This query avoids parameter sniffing by declaring and setting a new variable. Is this really a SQL Server 2005 work-around for the OPTIMIZE-FOR-UNKNOWN feature? Or am I missing something? (Authoritative links, answers or test results are appreciated).

More Info: A quick test on SQL Server 2008 tells me that the number of estimated rows in this query is in fact the same as if OPTIMIZE FOR UNKNOWN was specified. Is this the same behavior on SQL Server 2005? I think I remember hearing once that without more info, the SQL Server Optimizing Engine has to guess at the selectivity of the parameter (usually at 10% for inequality predicates). I'm still looking for definitive info on SQL 2005 behavior though. I'm not quite sure that info exists though...

More Info 2: To be clear, this question is asking for a comparison of the UNKNOWN query hint and the parameter-masking technique I describe.

It's a technical question, not a problem solving question. I considered a lot of other options and settled on this. So the only goal of this question was to help me gain some confidence that the two methods are equivalent.

Answer 1

I've used that solution several times recently to avoid parameter sniffing on SQL 2005 and it seems to me to do the same thing as OPTIMIZE FOR UNKNOWN on SQL 2008. Its fixed a lot of problems we had with some of our bigger stored procedures sometimes just hanging when passed certain parameters.