Hi Antonin, On Tue, Sep 10, 2019 at 4:31 PM Antonin Houska <a...@cybertec.at> wrote:
> Richard Guo <ri...@pivotal.io> wrote: > > > Can we try to pull up direct-correlated ANY SubLink with the help of > > LATERAL? > > > By this way, we can convert the query: > > > > select * from a where a.i = ANY(select i from b where a.j > b.j); > > > > To: > > > > select * from a SEMI JOIN lateral(select * from b where a.j > b.j) > > sub on a.i = sub.i; > > > > I tried this a few years ago. This is where the problems started: > > > https://www.postgresql.org/message-id/1386716782.5203.YahooMailNeo%40web162905.mail.bf1.yahoo.com Thank you for this link. Good to know the discussions years ago. > I'm not sure I remember enough, but the problem has something to do with > one > possible strategy to plan SEMI JOIN: unique-ify the inner path and then > perform plain INNER JOIN instead. > > I think the problemm was that the WHERE clause of the subquery didn't > participate in the SEMI JOIN evaluation and was used as filter instead. > Thus > the clause's Vars were not used in unique keys of the inner path and so the > SEMI JOIN didn't work well. > This used to be a problem until it was fixed by commit 043f6ff0, which includes the postponed qual from a LATERAL subquery into the quals seen by make_outerjoininfo(). Thanks Richard
