Re: bad estimates / non-scanning aggregates

On Thu, Aug 28, 2003 at 17:10:31 -0700,
Ken Geis <kgeis(at)speakeasy(dot)org> wrote:
> The query I want to run is
>
> select stock_id, min(price_date) from day_ends group by stock_id;

The fast way to do this is:

select distinct on (stock_id) stock_id, price_date
order by stock_id, price_date;

> Also, to get the MIN for a given group, not all values of the index need
> to be seen. Must pgsql do a full scan because it treats all aggregates
> in the same way? Are MIN and MAX used often enough to justify special
> treatment, and could that be cleanly implemented? Perhaps the aggregate
> function can request the data in a certain order, be told that it is
> being passed data in a certain order, and return before seeing the
> entire set of data.

Yes, max and min are not treated special so they don't benefit from
indexes. This has been discussed repeatedly in the archives.