Re: Using index with order desc

"Dave Smith" wrote:

> Using pg 7.2.1
>
> If I have a simple table transfer
>
> company_id int,
> module character(2)
> otherfields ...
>
> and an index
> CREATE INDEX transfer_5 on transfer(company_id,module);
>
> with the query
>
> explain select * from transfer where company_id=1012 order by
> company_id,module desc;
>
> I get ..
>
> NOTICE: QUERY PLAN:
>
> Sort (cost=462.74..462.74 rows=117 width=176)
> -> Index Scan using transfer_5 on transfer (cost=0.00..458.71
> rows=117 width=176)
>
>
> Why does it have to sort it? The desc is at the end and the first
> argument is constant. Is there some way I can force postgres to read the
> index backwards and save the sort step?
>

Try:

explain select * from transfer
where company_id=1012
order by company_id desc, module desc;

--
Peter Gibbs
EmKel Systems