On Tue, Oct 11, 2011 at 8:52 PM, Claudio Freire <klaussfreire@gmail.com> wrote:
> On Tue, Oct 11, 2011 at 5:16 PM, Carlo Stonebanks
> <stonec.register@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
