About FKs and indexes...

If a FK has Col1, Col2, Col3 by this order is a Col1, Col2 index any good?

It's probably better than nothing but should a Col1, Col2, Col3 index exist or a Col1, Col2, Col3, Col4, .... A Col1, Col2, Col4, Col3 probably is the same as just Col1, Col2 for a FK validation...

Thanks,

Pedro