Question

I’ll try to give an “eBay” example, I’m sure it will be the easiest way to ask this.

Imagine a table of bids:

bid_id | bid_from_user | bid_for_auction | bid_price
1      | 150           | 1               | 20
2      | 453           | 1               | 30
3      | 42            | 1               | 50
4      | 12            | 2               | 12
5      | 60            | 2               | 20

Imagine you need to list auctions which a certain person is currently bidding on and losing.

Therefore, our current user ID is 12, so bid_from_user='12'

This user is currently bidding on auction id 2 with price 12 and is obviously losing, as there is another user bidding on the same auction with a higher price.

I don’t want to list all the auctions the user is bidding on, I just want to list those the user is bidding on and losing (= not the ones he’s winning).

So, what query do I run to do this?

Answer 1

SELECT b.bid_id, b.bid_from_user, b.bid_for_auction, b.bid_price
  FROM bids b
 WHERE b.bid_from_user = '12'
   AND EXISTS (
           SELECT 1 
             FROM bids x 
            WHERE x.bid_for_auction = b.bid_for_auction
              AND x.bid_price > b.bid_price
              AND x.bid_from_user <> b.bid_from_user);

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Edit: The above would seem to be the cleanest, most legible solution; but here is an alternative in allowance for MySQL traditionally not handling subqueries well…

  SELECT b.bid_for_auction
    FROM bids b
         JOIN bids x ON x.bid_for_auction = b.bid_for_auction
     AND x.bid_price > b.bid_price
     AND x.bid_from_user <> b.bid_from_user
   WHERE b.bid_from_user = '12'
GROUP BY b.bid_for_auction;