On Mon, 20 May 2002, Wm. G. Urquhart wrote:
> Hi All,
>
> After yesterday's disaster I've taken this opportunity to rebuild by
> database from the ground up. As part of this I want to be able to set a
> column to have a default of 0 (easy enough) but this column is a Foreign
> Key to another table whos referenced column value starts at 1.
>
> Is there anyway I can write a FK Constraint that will allow this? I don't
> want to have to enter a row in the referenced table since since it in turn
> has not null constraints on it.
>
> I really want a way to allow 0 as a legitimate value, to assist in the
> predicates of a SELECT. It is possible to get to and modify the code that
> PostgreSQL creates to enforce this I assume via CREATE CONSTRAINT TRIGGER?
You could make a copy of the trigger functions in
backend/utils/adt/ri_triggers.c and change them to do what you want. I'm
assume that NULL in the foreign key table in unacceptable since a NULL
referencing column always works.