"Kevin Grittner" <Kevin.Grittner@xxxxxxxxxxxx> writes: > Marcin Miros*aw<marcin@xxxxxxxx> wrote: >> SELECT count(*) >> from (select * from users_profile order by id) u_p; >> "order by id" can be ignored by planner. > This has been discussed before. Certainly not all ORDER BY clauses > within query steps can be ignored, so there would need to be code to > determine whether it was actually useful, which wouldn't be free, > either in terms of planning time or code maintenance. It wasn't > judged to be worth the cost. If you want to avoid the cost of the > sort, don't specify ORDER BY where it doesn't matter. Considering that ORDER BY in a subquery isn't even legal per spec, there does not seem to be any tenable argument for supposing that a user wrote it there "by accident". It's much more likely that he had some semantic reason for it (say, an order-sensitive function in a higher query level) and that we'd break his results by ignoring the ORDER BY. I doubt that very many of the possible reasons for needing ordered output are reliably detectable by the planner, either. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
