It has been suggested to me that the use of IF statements in t-SQL batches is detrimental to performance. I'm trying to find some confirmation or validate this assertion. I'm using SQL Server 2005 and 2008.
The assertion is that with the following batch:-
IF @parameter = 0 BEGIN SELECT ... something END ELSE BEGIN SELECT ... something else END
SQL Server cannot re-use the execution plan generated because the next execution may need a different branch. This implies that SQL Server will eliminate one branch entirely from execution plan on the basis that for the current execution it can already determine which branch is needed. Is this really true?
In addition what happens in this case:-
IF EXISTS (SELECT ....) BEGIN SELECT ... something END ELSE BEGIN SELECT ... something else END
where it's not possible to determine in advance which branch will be executed?