SQL：最大汇总和按查询分组

Question

I am having troubles with my SQL query. I have the following Orders table

 id
 order_number_for_user
 user_id
 date

I want to select the most recent order for a user on a specific date (2015-01-19). Here is some sample data

 id| order_number_for_user | user_id |    created      
-------+---------------+---------+---------------
 1 |                     1 |      10 | 2015-01-19
 2 |                     2 |      10 | 2015-01-19
 3 |                     1 |      20 | 2015-01-19
 4 |                     1 |      30 | 2015-01-19
 5 |                     1 |      40 | 2015-01-19
 6 |                     2 |      40 | 2015-02-30

The correct output is the following row id's 2,3,4,5

Here is the broken query I built

SELECT id FROM orders WHERE order_number_for_user = 
(SELECT max(order_number_for_user) FROM orders as orders2 
WHERE orders.user_id=orders2.user_id 
AND date(created) = date('2015-01-19'))

The rows are selected by this query are 1,2,3,4,5 . Row 1 should not be selected since it is not the max order number for user 10 for the specified date.

Can someone please tell me how my query is incorrect?

Answer 1

You probably want this instead:

SELECT * 
FROM orders
WHERE id IN (
   SELECT MAX(id)
   FROM orders
   WHERE DATE(created) = '2015-01-19'
   GROUP BY user_id
) AS max_order_ids

The inner/subquery gets the maximum ID for every user's orders on that particular day. Then the outer query fetches the rest of the order information for those IDs.

Your query wasn't doing any grouping, so that MAX() aggregate has wonky results.

Answer 2

Use an INNER JOIN :

SELECT O1.id
FROM Orders AS O1
INNER JOIN (SELECT user_id, MAX(order_number_for_user) order_number_for_user 
            FROM Orders
            WHERE date(created) = date('2015-01-19')
            GROUP BY user_id) AS O2
    ON O1.user_id = O2.user_id
    AND O1.order_number_for_user = O2.order_number_for_user
WHERE date(O1.created) = date('2015-01-19')

Answer 3

You need a sub query to find all user_id and its max order, then your query will work as follow:

SELECT id FROM orders, (SELECT user_id, max(order_number_for_user) maxOrderNum FROM orders GRPOUP BY user_id) as orders2 where orders.user_id=orders2.user_id and orders.order_number_for_user = orders2.maxOrderNum AND orders.date(created) = date('2015-01-19'))