On Tue, Oct 11, 2011 at 8:52 PM, Claudio Freire <klaussfre...@gmail.com> wrote: > On Tue, Oct 11, 2011 at 5:16 PM, Carlo Stonebanks > <stonec.regis...@sympatico.ca> wrote: >> Question 2) Regardless of the answer to Question 1 - if another_id is not >> guaranteed to be unique, whereas pkey_id is – there any value to changing >> the order of declaration (more generally, is there a performance impact for >> column ordering in btree composite keys?) > > Multicolumn indices on (c1, c2, ..., cn) can only be used on where > clauses involving c1..ck with k<n.
I don't think that's true. I believe it can be used for a query that only touches, say, c2. It's just extremely inefficient. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
