Re: optimize query with a maximum(date) extraction

"hubert depesz lubaczewski" <depesz@depesz.com> writes:

> On Wed, Sep 05, 2007 at 12:30:21PM +0100, Gregory Stark wrote:
>> SELECT DISTINCT ON (id) id, the_date AS min_date FROM my_table ORDER BY id, the_date ASC
>> SELECT DISTINCT ON (id) id, the_date AS max_date FROM my_table ORDER BY id, the_date DESC
>> I think the first of these can actually use your index but the latter can't
>> unless you create one for it specifically (which is not so easy -- it'll be
>> easier in 8.3 though). Worse, I'm not really sure it'll be any faster than the
>> query you already have.
>
> it's easy to fix the second query (fix to use index) - just change order
> by to:
> order by id desc, the_date desc.

Cute. I didn't think of that, thanks

--
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com