> I had the idea to attach 1=2 to the users query, as in:
>
> select xxx
> from tableX
> where 1=2
>

Not really an answer to your question (because it already has been
answered), but rather a warning.

Firebird 1.5 does not optimise this query particularly well. It will
do a table scan and for each record evaluate whether 1=2.

Our PK fields are defined as a domain Integer (check > 0), so when we
need to ensure 0 records are returned, we use the following syntax.

select xxx
from tableX
where ID < 0

Firebird can then use the PK index with very little penalty. But if
you are just interested in the field names you can query them directly.

Adam