On Fri, 26 Dec 2008 10:43:25 -0800 David Fetter <da...@fetter.org> wrote:
> On Fri, Dec 26, 2008 at 03:34:33PM +0100, Ivan Sergio Borgonovo > wrote: > > I noticed that starting from 8.2 the documentation at > > http://www.postgresql.org/docs/8.2/interactive/sql-expressions.html > > say that multiple distinct expressions are supported > > > > aggregate_name (DISTINCT expression [, expression] ) > In 8.4, you'll be able to do: > WITH d AS ( > SELECT DISTINCT c1, c2 FROM table1 > ) > SELECT count(*) FROM d; Nice, but what will be the difference from select count(*) from (select distinct c1, c2 from t); ? Optimisation? Furthermore... I was actually looking at docs because I needed to find a way supported by both postgresql and mysql and I've heard that mysql is not that good at subselect and I doubt it supports WITH AS. (OK not really a postgresql problem...). Meanwhile what would you suggest as a general approach to stuff like select count(distinct c1, c2) from t; regardless of mysql support? and considering mysql support? I was thinking to find some way to exploit group by, but I didn't come to anything useful yet. > and very likely an OLAP version. :) What's "an OLAP version" of WITH d AS... -- Ivan Sergio Borgonovo http://www.webthatworks.it -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
