Hi Merlin, So should I interpret this as: there is a potential gain from choosing subqueries over with WITHs ?
On Tue, Feb 19, 2013 at 3:33 PM, Merlin Moncure <mmonc...@gmail.com> wrote: > On Tue, Feb 19, 2013 at 9:22 AM, Joe Van Dyk <j...@tanga.com> wrote: > > On Tue, Feb 19, 2013 at 1:02 AM, Albe Laurenz <laurenz.a...@wien.gv.at> > > wrote: > >> > >> Joe Van Dyk wrote: > >> > My assumption was that WITH acted just like subselects, but apparently > >> > they don't? Using WITH doesn't > >> > use the expected index. > >> > >> Currently WITH acts as an "optimization fence", that means > >> that means that the planner won't move conditions into or > >> out of the WITH query. > > > > > > Where's the best place to read up on this? > > Unfortunately, the mailing list archives. Rightly or wrongly, > postgresql docs are exceptionally light in terms of performance > aspects of various SQL mechanisms. > > (non-data modifying) WITH is basically formalization of technique: A > extract to temp table B query that table. Not the optimization fence > characteristic is an implementation detail and not future proofed but > is nevertheless widely replied upon. > > merlin > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general >
