From: Bruno Wolff III <bruno@wolff.to>
To: Achilleus Mantzios <achill@matrix.gatewaynet.com>
Cc: email lists <lists@darrenmackay.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: query not using index for descending records?
Date: Thu, 29 Jan 2004 08:06:55 -0600
Message-ID: <20040129140655.GA14885@wolff.to> (raw)
In-Reply-To: <Pine.LNX.4.44.0401291525350.9854-100000@matrix.gatewaynet.com>
References: <20040129131847.GE17068@wolff.to>
<Pine.LNX.4.44.0401291525350.9854-100000@matrix.gatewaynet.com>
On Thu, Jan 29, 2004 at 15:29:11 +0200,
Achilleus Mantzios <achill@matrix.gatewaynet.com> wrote:
> O kyrios Bruno Wolff III egrapse stis Jan 29, 2004 :
>
> As i see there was a thread
> http://archives.postgresql.org/pgsql-hackers/2003-05/msg00762.php
> dealing with this issue, assuming the "correct" order by
> should be "order by datetime ASC, id DESC".
So you really didn't want them in the reverse order?
> Do you know of any progress for declaring the direction of each
> column in a multicolumn index?
If you are using 7.4 you can use a functional index to get around this.
Assuming id is a numeric type, you can make an index on datetime and
(-id) and sort by datetime, -id and the index should get used.
This should still get fixed at some point, as this trick doesn't work
for types for which the - operator exists. But I haven't heard of
anyone working on it for 7.5, so don't expect a real fix any time soon.
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To: pgsql-sql@postgresql.org
Cc: bruno@wolff.to, achill@matrix.gatewaynet.com, lists@darrenmackay.com
Subject: Re: query not using index for descending records?
In-Reply-To: <20040129140655.GA14885@wolff.to>
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