Hello,
UNION will remove all duplicates, so that the result additionally requires to be sorted. Anyway, for performance issues, you should always start investigation with explain analyze . regards, Marc Mamin From: pgsql-performance-ow...@postgresql.org [mailto:pgsql-performance-ow...@postgresql.org] On Behalf Of Olivier Pala Sent: Donnerstag, 9. Dezember 2010 11:52 To: pgsql-performance@postgresql.org Cc: Olivier Pala Subject: [PERFORM] UNION and bad performance Hi, I have a performance trouble with UNION query First I have this view : SELECT a,b,c FROM table1, table2 WHERE jointure AND condition Result : 150 000 records in 1~2 s Then, I adding an UNION into the same view : SELECT a,b,c FROM table1, table2 WHERE jointure AND condition UNION SELECT a,b,c FROM table3 Result : 150 200 records in 6~7 s Why, do I have bad performance only for 200 adding records ? Thanks SGBD : Postgres 8.3 et 8.4
