>It's the EXISTS syntax. You don't have any row returned, it's only for
>syntax complinace. Ok, SELECT 1 works as well, but I prefer the general form.

Fine, we just have different preferences.

> > and a left join simply
> > means that the right table has no relevance within an EXISTS.
>
>Right, but that table is a stored procedure, that returns a value
>(OUT_DIFFERENZIA) that needs to be tested.
>It means "check if exixts one row that, in addition to some other
>criteria, if calls GET_CONTO_DIFFERENZIA_GR with it's data has a 'S' as
>OUT_PC_DIFF_GR"

OK, then I'll suggest you use (inner) JOIN rather than LEFT (outer) JOIN.

HTH,
Set