On Thu, Feb 21, 2013 at 4:31 AM, Seref Arikan <serefarikan@xxxxxxxxx> wrote: > Hi Merlin, > So should I interpret this as: there is a potential gain from choosing > subqueries over with WITHs ? Well, potentially, yes. WITH is a mechanic to force iterative order of evaluation on queries. This can be a good or bad thing naturally. Subqueries can also do this, especially if you put them in the field select list -- but WITH is more general. We also have an undocumented hack that uses OFFSET 0 to force subquery evaluation. These are all very dangerous tools because they tend to be very sensitive to data inputs as you are bypassing database statistics effectively. The other end of the spectrum is to use vanilla JOINs as much as possible -- this releases the work of planning the query to the database. Upcoming 9.3 LATERAL will remove one large class of cases where we have to do this: joining against set returning functions with non-constant inputs. merlin -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
