> --- In firebird-support@yahoogroups.com, "Ivan Prenosil"
> <Ivan.Prenosil@...> wrote:
> >
> > Since you use only one field in WHERE clause, adding another field
> to the index
> > can't speed up SELECT statement. Your problem is that either
> > - there are really too much 'Y' values in FALG field (thus dropping
> the index should help),
> >
> Sometimes there are millions of records with FLAG="Y" and sometimes
> only a few. As you point out, the index is not needed when a large
> percentage of the records have FLAG="Y". But when there are only a
> few it saves searching sequentially for that one-in-a-million record.
>
> >
> > or
> > - you have incorrect order of fields in index' definition, it must
> be (FLAG, PK), not (PK, FLAG)
> >
> I wish it were that easy. We have (FLAG, PK) :-(
>

if order is unimportant - then use an ORDER BY clause!!!
Alan