"Ivan Sergio Borgonovo" <mail@xxxxxxxxxxxxxxx> writes: > I'm reviewing some function I wrote to add stable, immutable where > needed and I'd like to take the chance to add further "cheap" > optimisation if it helps. > > There are many places where I know a function or a statement will > return just one row? > > Is it helpful to add LIMIT 1? > > eg. > select a, b from myfunction(3,5) limit 1; > select into a,b x,y from tablename where z=5 and u=7 limit 1; > select a,b from from tablename where z=5 and u=7 limit 1; In such simple queries the limit 1 won't do anything. In more complex queries it could help correct any problems higher up in the query caused by bad planner estimations. For example select * from a join (select x from myfunction(3,5) limit 1) as b(i) using (i) would work better than without the limit because without it the planner would have no idea that myfunction is only going to return 1 record. You could fix that more cleanly with "ALTER FUNCTION myfunction ROWS 1" but only if that's always true, not just for myfunction(3,5). -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's On-Demand Production Tuning -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
