Dimi Paun <dimi@xxxxxxxxxxx> writes: >> From what I've read on the net, these should be very similar, > and should generate equivalent plans, in such cases: > SELECT DISTINCT x FROM mytable > SELECT x FROM mytable GROUP BY x > However, in my case (postgresql-server-8.1.18-2.el5_4.1), > they generated different results with quite different > execution times (73ms vs 40ms for DISTINCT and GROUP BY > respectively): The results certainly ought to be the same (although perhaps not with the same ordering) --- if they aren't, please provide a reproducible test case. As for efficiency, though, 8.1 didn't understand how to use hash aggregation for DISTINCT. Less-obsolete versions do know how to do that. 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
