On Thu, May 14, 2009 at 4:52 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > "Brad Jorsch" <programmer@xxxxxxxxxxxxxxx> writes: >> But if I add a constant-valued column to indicate which branch of the >> union each result came from: > >> explain analyze select * from baz join ( >> select id, val, 'foo'::text as source from foo >> union all >> select id, val, 'bar'::text as source from bar >> ) as foobar on(baz.id2=foobar.id) where baz.id1=42; > >> All of a sudden it insists on a sequential scan (and takes 800 times as >> long to run) even when enable_seqscan is set false. Is there a good >> reason for this, or is it just a missed opportunity in the optimizer? > > It's an ancient and fundamental limitation that is fixed in 8.4. > Do not expect to see it fixed in 8.3.x. Does this also apply to the case of a join on an inherited table ? example: http://archives.postgresql.org/pgsql-performance/2003-10/msg00018.php Kind regards, Mathieu -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
