Re: limit results to one row per foreign object

[Martijn van Oosterhout <kleptog(at)svana(dot)org>]

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.

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