Ferda,

> Ann and Alex, thank you for your replies.
> What can be done about low-selective FK indices in this matter?

Firebird v2.0 introduces a new index storage structures (part of ODS
11).

The new storage structures have been specifically to resolve the problem
of low selectivity indices and also introduce new per-segment
selectivity information for multi-part indices to improve the optimizer
index selection.

So, what can you do? Wait for v2.0


Sean