Thanks very much to Milan, Adam, Helen, and Svein for your ideas on my
query. Several different approaches were suggested and I'll have to
play with them a bit to figure out which really fits my need better.

As I suspected, it's not a terribly difficult query but my SQL is
pretty rudimentary so this is a good learning experience for me.
Figuring out how each of the solutions really works will be very
enlightening!

Thanks again to the Firebird community for both a great tool and great
support!