On the same note:

I was once told that creating a forein-key constraint upon two tables causes an implicit creation of some indexes that can speed up joins on the FK relatoinship.

Does anyone know of this kind of index (it should be some kind of "cross-table"  or "relational" index)?

 If creating a FK does in fact cause creation of some kind of cross-table index, can the same kind of index be created without the FK constraints?

Many thanks,

 - Avi