Question

I am working on an auction web application. Now i have a table with bids, and from this table i want to select the last 10 bids per auction.

Now I know I can get the last bid by using something like:

SELECT bids.id FROM bids WHERE * GROUP BY bids.id ORDER BY bids.created

Now I have read that setting an amount for the GROUP BY results is not an easy thing to do, actually I have found no easy solution, if there is i would like to hear that.

But i have come up with some solutions to tackle this problem, but I am not sure if i am doing this well.

Alternative

The first thing is creating a new table, calling this bids_history. In this table i store a string of the last items.

example:

bids_history
================================================================
auction_id   bid_id     bidders               times
    1        20,25,40   user1,user2,user1     time1,time2,time3

I have to store the names and the times too, because I have found no easy way of taking the string used in bid_id(20,25,40), and just using this in a join.
This way i can just just join on auction id, and i have the latest result.

Now when there is placed a new bid, these are the steps:

• insert bid into bids get the lastinserteid
• get the bids_history string for this
  auction product
  • explode the string
  • insert new values
  • check if there are more than 3
  • implode the array, and insert the string again

This all seems to me not a very well solution.
I really don’t know which way to go. Please keep in mind this is a website with a lot of bidding’s, they can g up to 15.000 bidding’s per auction item. Maybe because of this amount is GROUPING and ORDERING not a good way to go. Please correct me if I am wrong.

After the auction is over i do clean up the bids table, removing all the bids, and store them in a separate table.

Can someone please help me tackle this problem!

And if you have been, thanks for reading..

EDIT

The tables i use are:

bids
======================
id      (prim_key)
aid     (auction id)
uid     (user id)
cbid    (current bid)
created (time created)
======================

auction_products
====================
id        (prim_key)
pid       (product id)
closetime (time the auction closses)

What i want as the result of the query:

result
===============================================
auction_products.id   bids.uid   bids.created
2                        6         time1
2                        8         time2
2                        10        time3
5                        3         time1
5                        4         time2
5                        9         time3
7                        3         time1
7                        2         time2
7                        1         time3

So that is per auction the latest bids, to choose by number, 3 or 10

Answer 1

Using user variable, and control flow, i end up with that (just replace the <=3 with <=10 if you want the ten auctions) :

SELECT a.*
FROM
 (SELECT aid, uid, created FROM bids ORDER BY aid, created DESC) a,
 (SELECT @prev:=-1, @count:=1) b
WHERE
 CASE WHEN @prev<>a.aid THEN
   CASE WHEN @prev:=a.aid THEN
    @count:=1
   END
 ELSE
   @count:=@count+1
 END <= 3