Re: limit results to one row per foreign object

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@magproductions.nl

magproductions b.v.

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