On Wed, Dec 29, 2010 at 7:34 AM, Simon Riggs <si...@2ndquadrant.com> wrote: > On Wed, 2010-12-29 at 07:17 -0500, Robert Haas wrote: >> > >> > Here I have a puzzle, why not choose the small table to build hash table? >> > It >> > can avoid multiple batches thus save significant I/O cost, isn't it? >> >> Yeah, you'd think. Can you post a full reproducible test case? > > It's not a bug, that's the way it currently works. We don't need a test > case for that. > > I agree that the optimisation would be a useful one. > > It allows you to ask the query "Show me sales for each of my stores" > efficiently, rather than being forced to request the inner join query > "Show me the sales for each of my stores for which there have been > sales", which is a much less useful query.
Oh, you're right. I missed the fact that it's a left join. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
