Left To Right Evaluation Question

I am trying to rewrite a stored procedure that right now works by string concatination.

I would like to mimic that in sql, and have therefore made something that looks like this:





Code Block
declare @guard varchar(20)
set @guard = ''

select *
from Table1
where @guard = '' or
pk in (select pk from Table2)







What I really would have liked was that the guard worked, and Table2 therefore never was searched (because of left to right evaluation), but when I look in the execution plan then I can see that Table2 is getting it's clustered index scan every time.

Does anyone have a good explanation for this, and mabye a good idea on how I can achive what I want?

I work in mssql server 2000.