Re: query not using index for descending records? - Mailing list pgsql-sql

From Achilleus Mantzios
Subject Re: query not using index for descending records?
Date
Msg-id Pine.LNX.4.44.0401291657210.10019-100000@matrix.gatewaynet.com
Whole thread Raw
In response to Re: query not using index for descending records?  (Bruno Wolff III <bruno@wolff.to>)
List pgsql-sql
O kyrios Bruno Wolff III egrapse stis Jan 29, 2004 :

> 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?

I am not the initiator of this thread,
i was just lurking :)

> 
> > 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.
> 

It would be nice to have this feature for varchar as well.

> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
>       subscribe-nomail command to majordomo@postgresql.org so that your
>       message can get through to the mailing list cleanly
> 

-- 
-Achilleus



pgsql-sql by date:

Previous
From: "Alexandra Birch"
Date:
Subject: Re: limit 1 and functional indexes
Next
From: "Chris Travers"
Date:
Subject: How to retrieve N lines of a text field.