Обсуждение: referencing system catalogs
Can someone explain the reasoning behind not allowing a user table to contain a foreign key of a system table? For example: create table myusers ( login text references pg_catalog.pg_shadow(usename), ... ); Fails with a message about using system catalogs. Using pg_user fails because it is a view and not a table. Is it because updates to the catalogs can be done outside of transactions? Is that a good enough reason? thanks, elein ============================================================ elein@varlena.com Varlena, LLC www.varlena.com PostgreSQL Consulting, Support & Training PostgreSQL General Bits http://www.varlena.com/GeneralBits/ ============================================================= I have always depended on the [QA] of strangers.
On Sat, 26 Jun 2004, elein wrote: > Can someone explain the reasoning behind not allowing > a user table to contain a foreign key of a system table? > > For example: > > create table myusers ( > login text references pg_catalog.pg_shadow(usename), > ... > ); > > Fails with a message about using system catalogs. > Using pg_user fails because it is a view and not a table. > > Is it because updates to the catalogs can be done outside > of transactions? Is that a good enough reason? I believe it's because changes to at least some of the system catalogs can be done without going through the entire sequence that an update/insert/delete statement would (ie, the triggers might not be fired thus meaning the constraint isn't properly checked).