Re: limit results to one row per foreign object

If you don't mind using a (quite useful) postgres extension, this might
work for you:

select distinct on (auctions.id, users.id) *
from auctions, bids, users
where <join clauses>
order by auctions.id, users.id, created_at desc;

Hope this helps,

On Fri, Jun 30, 2006 at 04:13:12PM +0100, Alan Bullock wrote:
> hi all, I have the following schema:
>
> CREATE TABLE auctions ( id serial NOT NULL, user_id int4, title
> varchar(255), body varchar(255), CONSTRAINT auctions_pkey PRIMARY KEY (id) )
> WITHOUT OIDS;
>
> CREATE TABLE bids ( id serial NOT NULL, auction_id int4, user_id int4,
> amount float8, created_at timestamp, CONSTRAINT bids_pkey PRIMARY KEY (id) )
> WITHOUT OIDS;
>
> CREATE TABLE users ( id serial NOT NULL, username varchar(255), CONSTRAINT
> users_pkey PRIMARY KEY (id) ) WITHOUT OIDS;
>
> I'd like to return all the bids for a given auction, but limit it to only
> the *latest* bid from each user. so regardless of how many bids a user has
> placed, only their latest is returned.
>
> I dont have a clue where to even start with this and would appreciate some
> pointers
> thanks
>
> alan
>
>
>
>
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Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.