On Fri, Nov 12, 2010 at 10:25:51AM -0500, Tom Lane wrote: > Yeb Havinga <yebhavi...@gmail.com> writes: > > On 2010-11-11 17:50, Marko Tiikkaja wrote: > >> Just to be clear, the main point is whether they see the data > >> modifications or not. The simplest case to point out this behaviour is: > >> > >> WITH t AS (DELETE FROM foo) > >> SELECT * FROM foo; > >> > >> And the big question is: what state of "foo" should the SELECT > >> statement see? > > > Since t is not referenced in the query, foo should not be deleted at > > all, > > Yeah, that's another interesting question: should we somehow force > unreferenced CTEs to be evaluated anyhow?
Yes. > Now that I think about it, > there was also some concern about the possibility of the outer query > not reading the CTE all the way to the end, ie > > WITH t AS (DELETE FROM foo RETURNING *) > SELECT * FROM t LIMIT 1; > > How many rows does this delete? I think we concluded that we should > force the DELETE to be run to conclusion even if the outer query didn't > read it all. Yes. > From an implementation standpoint that makes it more > attractive to do the DELETE first and stick its results in a tuplestore > --- but I still think we should view that as an implementation detail, > not as part of the specification. Right :) Cheers, David. -- David Fetter <da...@fetter.org> http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: david.fet...@gmail.com iCal: webcal://www.tripit.com/feed/ical/people/david74/tripit.ics Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
