I did exactly that, using the small example, you find that the datediff and dateadd are nearly identical, indexes or not. So I grabbed a large table (a few million rows) from our systems, indexed them appropriately and ran a few tests. When comparing my three tests, datediff ranked at 90%, dateadd, although a complex plan, took only 9%, and the final test took the remaining 1%. What we typically do for tables which are queried on a datetime field religiously is to actually create another column with the date portion only. It does require an extra 4 bytes (smalldatetime) per row, but disk space is cheap. Just remember to update the column after the data load in a batch update statement, don't use triggers, computed columns, or calcs in your inserts, as this will slow your data loads down drastically.