Hi Set,

> I don't (yet) agree with Adam and don't think there's any point in
> changing to a NOT EXISTS ('yet' indicating that I don't use Fb 2.0
> myself, and that he might have knowledge that I have missed).

Check the Firebird 2 release notes printed page number 102.

[quote]
Performance

The following changes should be noted as possible sources of
performance loss:

Existence Predicates NOT IN and ALL May Be Slow

Firebird and, before that, InterBase, have produced incorrect results
for the logical existence predicates ALL and NOT IN for many years.
That problem has bee corrected in Firebird 2.0, but the change means
that indexes on the inner tables cannot be used and performance may be
slow compared to the same query's performance in V.1.5. "Inner tables"
are the tables used in the subquery argument inside an ALL or NOT
IN expression.

Note

NOT EXISTS is approximately equivalent to NOT IN and will allow
Firebird to use indexes.

[/quote] (sic)


Adam