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Re: Can't use subselect in check constraint

From: "Gregory Wood" <gregw(at)com-stock(dot)com>
To: "PostgreSQL-General" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Can't use subselect in check constraint
Date: 2001-12-20 21:46:29
Message-ID: 046601c1899f$f4e46a20$7889ffcc@comstock.com (view raw or flat)
Thread:
Lists: pgsql-general
> > Is this something that will change anytime soon?  I could not find
anything about it in the todo...
>
> My understanding is that check constraints can't be queries;  at least I
> have never seen them.

Considering that you could potentially have to reevaluate each CHECK
constraint every time you updated any table in the database, I would think
it would be a *real* bad idea to allow that. There is no way to
automatically create the triggers needed to satisfy "When should I check the
constraint?"

If it can't be constructed as a check against a literal value or values, or
a foreign key constraint, it should be up to the user to maintain that
consistency check with the appropriate triggers.

Greg


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