On Tue, 2008-09-09 at 13:45 +0900, Tatsuo Ishii wrote: > Thanks for the review. > > > The standard specifies that non-recursive WITH should be evaluated > > once. > > What shall we do? I don't think there's a easy way to fix this. Maybe > we should not allow WITH clause without RECURISVE?
My interpretation of 7.13: General Rules: 2.b is that it should be single evaluation, even if RECURSIVE is present. The previous discussion was here: http://archives.postgresql.org/pgsql-hackers/2008-07/msg01292.php The important arguments in the thread seemed to be: 1. People will generally expect single evaluation, so might be disappointed if they can't use this feature for that purpose. 2. It's a spec violation in the case of volatile functions. 3. "I think this is a "must fix" because of the point about volatile functions --- changing it later will result in user-visible semantics changes, so we have to get it right the first time." I don't entirely agree with #3. It is user-visible, but only in the sense that someone is depending on undocumented multiple-evaluation behavior. Tom Lane said that multiple evaluation is grounds for rejection: http://archives.postgresql.org/pgsql-hackers/2008-07/msg01318.php Is there hope of correcting this before November? > I will try to fix this. However detecting the query being not a > non-linear one is not so easy. If we don't allow mutual recursion, the only kind of non-linear recursion that might exist would be multiple references to the same recursive query name in a recursive query, is that correct? > > * DISTINCT should supress duplicates: > > > > with recursive foo(i) as > > (select distinct * from (values(1),(2)) t > > union all > > select distinct i+1 from foo where i < 10) > > select * from foo; > > > > This outputs a lot of duplicates, but they should be supressed > > according to the standard. This query is essentially the same as > > supporting UNION for recursive queries, so we should either fix both for > > 8.4 or block both for consistency. > > I'm not sure if it's possible to fix this. Will look into. > Can't we just reject queries with top-level DISTINCT, similar to how UNION is rejected? > > * outer joins on a recursive reference should be blocked: > > > > with recursive foo(i) as > > (values(1) > > union all > > select i+1 from foo left join (values(1)) t on (i=column1)) > > select * from foo; > > > > Causes an infinite loop, but the standard says using an outer join > > in this situation should be prohibited. This should be fixed for 8.4. > > Not an issue, I think. Agreed, Andrew Gierth corrected me here. Regards, Jeff Davis -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
