On Fri, 2009-07-10 at 09:46 -0400, Bruce Momjian wrote: > 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? You don't. I was assuming that you could already prove that each subquery was distinct in itself. It's one for the TODO, that's all. I see it often, but I'm not planning to work on the code for this myself. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Training, Services and Support -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
