On Wed, Oct 18, 2006 at 03:32:15PM -0700, Jeff Davis wrote: > On Wed, 2006-10-18 at 17:10 -0500, Jim C. Nasby wrote: > > Sorry, don't have the earlier part of this thread, but what about... > > > > SELECT greatest(max(a), max(b)) ... > > > > ? > > To fill you in, we're trying to get the max of a union (a view across > two physical tables). UNION or UNION ALL? You definitely don't want to do a plain UNION if you can possibly avoid it. > It can be done if you're creative with the query; I suggested a query > that selected the max of the max()es of the individual tables. Your > query could work too. However, the trick would be getting postgresql to > recognize that it can transform "SELECT max(x) FROM foo" into that, > where foo is a view of a union. > > If PostgreSQL could sort the result of a union by merging the results of > two index scans, I think the problem would be solved. Is there something > preventing this, or is it just something that needs to be added to the > planner? Hrm... it'd be worth trying the old ORDER BY ... LIMIT 1 trick just to see if that worked in this case, but I don't have much hope for that. -- Jim Nasby jim@xxxxxxxxx EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
