Re: limit results to one row per foreign object

[Alban Hertroys <alban(at)magproductions(dot)nl>]

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

Hmm... No foreign key constraints?

I think you're looking for something like:

SELECT *
  FROM bids
 WHERE auction_id = 1234
 GROUP BY user_id
 HAVING created_at = MAX(created_at);

You could also use a subselect with an order by created_at DESC limit 1 
over each users bids.

Regards,

--
Alban Hertroys
alban(at)magproductions(dot)nl

magproductions b.v.

T: ++31(0)534346874
F: ++31(0)534346876
M:
I: www.magproductions.nl
A: Postbus 416
   7500 AK Enschede

// Integrate Your World //