Re: query not using index for descending records?

On Thu, Jan 29, 2004 at 15:29:11 +0200,
Achilleus Mantzios <achill(at)matrix(dot)gatewaynet(dot)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.