Enable execution plan (control-m) and run both in the same query window. It will show you the relative costs and query plans. Examine the different query plans to see what is different. Is it just the query that you have shown that you are running, or is there more to it? Is it part of a stored procedure? If it is part of a stored procedure (or even if it is not), you can try statement level recompilation hint (add OPTION (RECOMPILE) at the end of the statement) to see if that makes any difference.