On Fri, Apr 3, 2009 at 9:17 AM, Matthew Wakeling <matthew@xxxxxxxxxxx> wrote: > > So, I have a view. The query that the view uses can be written two different > ways, to use two different indexes. Then I use the view in another query, > under some circumstances the first way will be quick, and under other > circumstances the second way will be quick. > > What I want to know is, can I create a view that has both queries, and > allows the planner to choose which one to use? The documentation seems to > say so in http://www.postgresql.org/docs/8.3/interactive/querytree.html (the > rule system "creates zero or more query trees as result"), but doesn't say > how one would do it. yes. create view v as select * from ( select true as b, pg_sleep(1)::text union all select false as b, pg_sleep(1)::text ) q; recent versions of pg are smart enough to optimize (in some cases): select * from v where b; merlin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
