If you look up Table Hints in Books Online, you’ll find the following statement:
If a clustered index exists, INDEX(0) forces a clustered index scan and INDEX(1) forces a clustered index scan or seek.
If no clustered index exists, INDEX(0) forces a table scan and INDEX(1) is interpreted as an error.
The interesting thing there is that both hints can result in a scan. If that is the case, you might wonder if there is any effective difference between the two. This blog entry explores that question, and highlights an optimizer quirk that can result in a much less efficient query plan when using INDEX(0). I’ll also cover some stuff about ordering guarantees. Read More...