Simon Riggs wrote: > or a query like this > > Select '1', ... > ... > union > Select status, ... > ... > where status != '1'; > ; > > then it is clear that we could automatically prove that the the distinct > step is redundant and so we could either hash or sort. This is the same > as replacing the UNION with UNION ALL. In the last example, how do you know that status != '1' produces unique output? I assumed UNION gave distinct for the entire output, not just remove duplicates from the two UNION branches; that's how Postgres behaves now: test=> SELECT 1 UNION (SELECT 2 UNION ALL SELECT 2); ?column? ---------- 1 2 (2 rows) -- Bruce Momjian <bruce@xxxxxxxxxx> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
