>This is really helpful. Now I realize that my statement in the post where I said that I thought not in and not exists were functionally equivalent, is wrong. This is a much better explanation of why not to use "IN" than the post that Nadia referenced. (Thanks anyway though Nadia)
>
>I still don't understand though why exists works. What is it functionally equivalent to? Why doesn't it care about nulls?
>

The EXISTS only checks if a record exists thet satisfies the conditions. It does not return any data.