так у них баг конкретный получился
если на поле varchar поставить CONSTRAINT CHECK (pole <> '') тогда невозможно сделать UPDATE для конкретной записи или для всей базы
Ругается...
Это пока всё что я нашёл...

UPDATED 2006-02-06 22:14 UTC

The PostgreSQL Global Development Group releases today a security update older PostgreSQL versions: minor versions 8.0.11, 7.4.16 and 7.3.18. Because this patches a medium-risk security hole, all users of 8.0, 7.4 and 7.3 are urged to upgrade at the earliest opportunity.

Security Releases for versions 8.1 and 8.2 are still pending. Previously released source for 8.2.2 and 8.1.7 has been WITHDRAWN due to a bug with typemod data types used with check constraints and expression indexes. New minor versions of 8.2 and 8.1 will be re-released within 24 to 48 hours.

http://]http://www.postgresql.org/about/news.741