Scott Marlowe <scott.marlowe@xxxxxxxxx> writes: > On Wed, Jul 1, 2009 at 11:52 AM, Tom Lane<tgl@xxxxxxxxxxxxx> wrote: >> Scott Marlowe <scott.marlowe@xxxxxxxxx> writes: >>> Sometimes putting a where clause portion into the on clause helps. >>> like: >>> select * from a left join b on (a.id=b.id) where a.somefield=2 >>> might run faster with >>> select * from a left join b on (a.id=bid. and a.somefield=2); >>> but it's hard to say. >> >> Uh, those are not the same query ... they will give different results >> for rows with a.somefield different from 2. > How so? Neither should return any rows with a.somefield <> 2. Wrong. The second will return rows with somefield <> 2, null-extended (whether or not there is any match on id). regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
