On Thu, Mar 5, 2009 at 11:25 PM, Christian Schröder <cs@xxxxxxxxx> wrote: > Hi list, > if I want to find all records from a table that don't have a matching record > in another table there are at least two ways to do it: Using a left outer > join or using a subselect. I always thought that the planner would create > identical plans for both approaches, but actually they are quite different > which leads to a bad performance in one case. > I tried the following test case: SNIP > All tests have been performed on a PostgreSQL 8.2.9 server: Have you looked at the release notes for 8.2.12? Especially this line: Fix planner misestimation of selectivity when transitive equality is applied to an outer-join clause (Tom) This could result in bad plans for queries like ... from a left join b on a.a1 = b.b1 where a.a1 = 42 ... -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
