> I think the basic problem would be what the check constraint subquery > meant to the user, and how useful that is expected to be in general. A > subquery in a check constraint would presumably involve checking the > subquery using an existing snapshot of the command that required the > constraint to be verified (say, an INSERT). But why should that > snapshot be so special? In any case the result of the subquery may not > be immutable (even in some limited, practical sense), and we expect > check constraints to be on immutable conditions on constrained columns > only. In general it would be practically impossible to determine that > something else had changed the state of the database in such a way as > to make the check constraint no longer verify successfully on each > row, so we would not be able to prevent that from happening later on. > > I imagine that you have a very specific case in mind, though. Perhaps > you can share the details.
No I don't have a specific case. I am just wondering because it's defined in the standard. Best regards, -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers