根据另一个表中没有子行更新表的列值

Question

I have an "items" table:

item_id |      expiration       | status 
------------------------------------------
   1    |  2014-04-02 12:00:00  |  NULL
   2    |  2014-04-01 17:00:00  |  NULL
   3    |  2014-03-31 17:30:00  |  NULL
   4    |  2014-04-14 19:00:00  |  NULL

and an "bids" table:

 bid_id  | item_id | withdrawn | amount
---------------------------------------
   1     |    1    |    NULL   |   10
   2     |    1    |    NULL   |   20
   3     |    1    |    NULL   |   30
   4     |    2    |     1     |   15
   5     |    4    |    NULL   |   10

The item_id column in the bids table is the child of item_id in the items table.

I need to figure out an UPDATE query that does one of two things:

1. Adds 7 days to expiration if the item is expired (expiration < NOW()) and there are no bids for it in the bids table.
2. Or updates the item's status to sold if the item is expired and there are bids for it in the bids table.

So given the data in the two tables above and today's date of 4/4/14, the results of the update query I need would:

1. Update the status of item 1 to sold (since it has expired and there are bids for it) .
2. Add 7 days to the expiration of item 2 (since it has expired and the only bid for it was withdrawn) .
3. Add 7 days to the expiration of item 3 (since it has expired and there are no bids for it) .
4. Ignore item 4 (since it has not yet expired) .

Anyway, I'm having trouble trying to figure out the proper query. Any help would be greatly appreciated. Thanks for taking the time.

Best, Josh

Answer 1

Both parts together.

UPDATE items a 
    LEFT JOIN bids b
      ON a.item_id = b.item_id
        and b.withdrawn IS NULL
SET a.expiration = CASE WHEN b.bid_id IS NULL
                        THEN DATE_ADD(a.expiration,INTERVAL 7 DAY) 
                        ELSE a.expiration
                   END,
    a.status = CASE WHEN b.bid_id IS NOT NULL
                    THEN 'sold'
                    ELSE a.status
               END
WHERE expiration < NOW();

SQL FIDDLE DEMO

Answer 2

Here is what I did:

1.Adds 7 days to expiration if the item is expired (expiration < NOW()) and there are no bids for it in the bids table.

update items set expiration = timestampadd(day, 7, expiration) where expiration < now()
and 0 = (select count(*) from bids where bids.item_id = items.item_id and isnull(withdrawn) );

2.Or updates the item's status to sold if the item is expired and there are bids for it in the bids table.

update items set status = "sold" where expiration < now()
and 0 < (select count(*) from bids where bids.item_id = items.item_id and isnull(withdrawn) );

Answer 3

Part I:

UPDATE I
  SET expiration = DATE_ADD(I.expiration,INTERVAL 7 DAY)
FROM Items AS I
WHERE I.expiration < NOW() 
  AND NOT EXISTS(SELECT * FROM Bids AS B WHERE B.item_id = I.item_id AND B.Withdrawn IS NULL)

Part II:

UPDATE I
  SET Status = 'Sold'
FROM Items AS I
WHERE I.expiration < NOW() 
  AND EXISTS(SELECT * FROM Bids AS B WHERE B.item_id = I.item_id AND B.withdraw IS NULL)