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Re: Indexes with descending date columns

From: Theo Kramer <theo(at)flame(dot)co(dot)za>
To: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Indexes with descending date columns
Date: 2006-03-29 10:52:31
Message-ID: 1143629550.2985.29.camel@theo-laptop.int.coza.net.za (view raw or flat)
Thread:
Lists: pgsql-performance
On Fri, 2006-03-24 at 12:21, Jim C. Nasby wrote:
> On Thu, Mar 23, 2006 at 01:09:49PM +0200, Theo Kramer wrote:
> > ii If no to i, is it feasible to extend PostgreSQL to allow traversing
> >    an index in column descending and column ascending order - assuming
> >    an order by on more than one column with column order not 
> >    in the same direction and indexes existing? ... if that makes sense.
> 
> Yes.
> 
> stats=# explain select * from email_contrib order by project_id desc, id desc, date desc limit 10;
>                                                        QUERY PLAN                                                       
> ------------------------------------------------------------------------------------------------------------------------
>  Limit  (cost=0.00..31.76 rows=10 width=24)
>    ->  Index Scan Backward using email_contrib_pkey on email_contrib  (cost=0.00..427716532.18 rows=134656656 width=24)
> (2 rows)

Not quite what I mean - redo the above as follows and then see what
explain returns

explain select * from email_contrib order by project_id, id, date desc
limit 10;

-- 
Regards
Theo


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