On Thu, May 25, 2006 at 16:31:40 -0400, Merlin Moncure <mmoncure@xxxxxxxxx> wrote: > On 5/25/06, Bruno Wolff III <bruno@xxxxxxxx> wrote: > >On Thu, May 25, 2006 at 16:07:19 -0400, > > Merlin Moncure <mmoncure@xxxxxxxxx> wrote: > >> been doing a lot of pgsql/mysql performance testing lately, and there > >> is one query that mysql does much better than pgsql...and I see it a > >> lot in normal development: > >> > >> select a,b,max(c) from t group by a,b; > >> > > >SELECT DISTINCT ON (a, b) a, b, c FROM t ORDER BY a DESC, b DESC, c DESC; > > that is actually slower than group by in my case...am i missing > something? (both essentially resolved to seq_scan) If there aren't many c's for each (a,b), then a sort might be the best way to do this. I don't remember if skip scanning ever got done, but if it did, it would have been 8.1 or later.
