Helen and Sean,
two small corrections below.

> LIKE does not use an index, whereas STARTING WITH does.

"like 'A%'" and "starting 'A'" are equivalent, AFAIK.

[Note: "like ?" and "starting ?" are not equivalent, though, even when
the parameters are 'A%' and 'A'.]

Anyway Sean said he has the fields in the where clause indexed
(don't know whether he means just the join fields or the F field too).

> Also, that framework has ambiguous syntax: Firebird will not buy it
> without a table identifier on column F.

unless you have F on more than one table, Firebird will accept it
without
complaints.

Sean,
I would like to have a look at the access plan for both queries; knowing
from which table does F come from would help too.
Ciao
--
____
_/\/ando