SQL-从子查询中提取列

Question

I'm working on a database meant for auctions and I would like get the id of all the winning bids. The hard part is extracting it from a subquery that returns 2 columns: the id and the amount. It looks something like this: SELECT id FROM Bid WHERE id IN (Select ID,max(amount) FROM Bid group by bid.idAuction)

Can I somehow extract just one column from the subquery? Any other sugestions to do this task are helpfull too.

Thank you!

Answer 1

Your query is close, but you need a correlated subquery to make this work:

SELECT b.id
FROM Bid b
WHERE b.amount = (SELECT max(amount)
                  FROM Bid b2 
                  WHERE b2.idAuction = b.idAuction
                 );

Answer 2

SELECT id, maxBid.MAmount, Bid.Amount
FROM Bid 
INNER JOIN (Select ID,max(amount) mamount FROM Bid group by bid.idAuction) MaxBid
 on MaxBid.ID = Bid.ID

RDBMS and SQL operate most effectively in SET based operations. So in this case we generate a set based on ID and max bid. We then join it back to the base set so that only the max bids are treturned.