CREATE TABLE docs fix - Mailing list pgsql-patches

This patch fixes a minor inaccuracy in the documentation: NOT NULL is
not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider
ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check
constraint.

Cheers,

Neil

--
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC