Evgeniy Shishkin <itparanoia@xxxxxxxxx> writes: >> select * from users join notifications on users.id=notifications.user_id ORDER BY users.priority desc ,notifications.priority desc limit 10; > In my understanding, i need to have two indexes > on users(priority desc, id) > and notifications(user_id, priority desc) > then postgresql would choose nested loop and get sorted data from indexes. > But it wont. Indeed. If you think a bit harder, you'll realize that the plan you suggest would *not* produce the sort order requested by this query. It would (if I'm not confused myself) produce an ordering like users.priority desc, id asc, notifications.priority desc which would only match what the query asks for if there's just a single value of id per users.priority value. Offhand I think that the planner will not recognize a nestloop as producing a sort ordering of this kind even if the query did request the right ordering. That could perhaps be improved, but I've not seen many if any cases where it would be worth the trouble. 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
