Re: Getting pk of the most recent row, in a group by

On Aug 13, 2007, at 15:05 , Bryce Nesbitt wrote:

> # select type,min(expires),count(*) from coupon group by type;
> type | min | count
> ------+------------+-------
> free | 2007-01-01 | 4 ; pk=1
> 50% | 2008-06-01 | 3 ; pk=5
>
> In the second example, is it possible to get the primary key of the
> row
> with the minimum expires time?

I believe DISTINCT ON will do what you want, if you don't mind using
non-SQL-spec functionality:

SELECT DISTINCT ON (type)
type, expires, coupon_id
FROM coupon
ORDER BY type, expires;

I believe you'd need to add the COUNT using a join:

SELECT type, expires, coupon_id, type_count
FROM (
SELECT DISTINCT ON (type)
type, expires, coupon_id
FROM coupon
ORDER BY type, expires
) earliest_to_expire
JOIN (
SELECT type, count(coupon_id) as type_count
FROM coupons
GROUP BY type
) type_counts USING (type);

Michael Glaesemann
grzm seespotcode net