Martijn van Oosterhout <kleptog@xxxxxxxxx> writes: > I've having a smaller planner problem (server version 8.3.5). I have a > table with revisions (revs) and I have a view on top of that gives the > latest revision of each rule. When I request a specific rule, it works > fine. > ... > But when I want to join on this view, it all goes pear shaped, as can > be seen in the following (completely equivalent) query: > # explain select * from maxrevs where rul_id=ANY(select rul_id from rules where rul_sid=15895); There isn't any provision in the planner for trying to exchange the order of a join and a GROUP BY operation. In the general case it wouldn't even be allowed anyway since it'd change the results. In this specific case --- semijoin using an equality condition on the grouping key --- I agree that it would be a legitimate transformation. But it's not obvious that it would be a win. I think if we wanted to consider it we'd have to develop plans both ways and compare costs. And that would be a really major amount of work. The simpler case isn't treated as a join, just a simple WHERE condition on individual rows, so it does what you want. I think you'll have to write out your queries without benefit of the view :-(. Sorry the news isn't better. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
