> > Consider this query on a large table with lots of different IDs: > > SELECT id FROM my_table GROUP BY id ORDER BY count(id) LIMIT 10; > > It has an index on id. Obviously, the index helps to evaluate count(id) > for a given value of id, but count()s for all the `id's should be > evaluated, so sort() will take most of the time. > > Is there a way to improve performance of this query? If not, please > give some indication to do a workaround on the source itself, so perhaps > I may be able to come out with a patch. > Is there a difference in performance if you re-write it as
SELECT id, count(id) FROM my_table GROUP BY id ORDER BY 2 LIMIT 10 ; ? Regards, Christoph ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
