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

Do you have a table of coupon types?

Terry

Terry Fielder
terry@greatgulfhomes.com
Associate Director Software Development and Deployment
Great Gulf Homes / Ashton Woods Homes
Fax: (416) 441-9085



Bryce Nesbitt wrote:
> I've got a table of "coupons" which have an expiration date.  For each
> type of coupon, I'd like to get the primary key of the coupon which will
> expire first. 
>
> # create table coupon
> (
>         coupon_id serial primary key,
>         type varchar(255),
>         expires date
> );
> insert into coupon values(DEFAULT,'free','2007-01-01');
> insert into coupon values(DEFAULT,'free','2007-01-01');
> insert into coupon values(DEFAULT,'free','2007-06-01');
> insert into coupon values(DEFAULT,'free','2007-06-01');
> insert into coupon values(DEFAULT,'50%','2008-06-01');
> insert into coupon values(DEFAULT,'50%','2008-06-02');
> insert into coupon values(DEFAULT,'50%','2008-06-03');
>
> The desired query would look like:
>
> # select coupon_id,type,expires from coupon where type='free' order by
> expires limit 1;
>  coupon_id | type |  expires  
> -----------+------+------------
>          1 | free | 2007-01-01
>
>
> But be grouped by type:
>
> # 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?
>
>