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. So, an index on (a,b) does *not* help for querying on b. Furthermore, if a is unique, querying on a or querying on a and b is equally selective. b there is just consuming space and cpu cycles. I'd say, although it obviously depends on the queries you issue, you only need an index on another_id. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
