Question

I have this query (notice that all 3 subqueries are selecting different columns from the same row). Essentially I want to get the rows in product_bid with the maximum date alongside the product row.

SELECT 
p.product_id,
p.product_title, 
(SELECT b.bid_id FROM product_bids b WHERE b.bid_product_id=p.product_id ORDER BY b.bid_date DESC LIMIT 1) AS bid_id,
(SELECT b.bid_date FROM product_bids b WHERE b.bid_product_id=p.product_id ORDER BY b.bid_date DESC LIMIT 1) AS bid_date,
(SELECT b.bid_amount FROM product_bids b WHERE b.bid_product_id=p.product_id ORDER BY b.bid_date DESC LIMIT 1) AS bid_amount

FROM product p

WHERE p.product_auction_id=325

Is there a way to do the subquery once to get the PK of product_bids, and join on that (the result of the subquery) or any clean way of doing this?

Side Note: Would the query optimiser recognise this anyway, making it less important?

Thanks

Answer 1

You can join your tables together with a subquery that selects the latest bid date for each product:

SELECT p.product_id, b.bid_id, b.bid_date, b.bid_amount
FROM   product_bids AS b NATURAL JOIN (
         SELECT   bid_product_id, MAX(bid_date) AS bid_date
         FROM     product_bids
         GROUP BY bid_product_id
       ) AS t
  JOIN product AS p ON p.product_id = b.bid_product_id
WHERE  p.product_auction_id = 325