Helen,

> I think it is very bizarre to make a composite primary key on the detail table AND to make one of the columns of that key your foreign key. What is your reasoning for that? What does WONO add that BMNO doesn't do on its own?

WONO adds referential integrity. It guarantees that a record in
BILLOFMATERIAL having a non-existent WONO will never be part of the
relation.
if I'm not mistaken, this is the "classic" (maybe obsolete) way of
structuring master/detail relationships. It may not be desirable for
performance and/or strictly firebird-related reasons, but from a design
point of view I don't see it as bizarre as you do.
WRT the original problem, I guess Paul's suggestion will do.
Ciao
--
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_/\/ando