选择每个用户的最后一个条目

Question

I have a TABLE user_orders with fields -->

• order_id int(10),
• user_id int(10),
• order_payment_id int(10)
• order_created int(10)

I want to find the last order_payment_id used for each user_id. I try

SELECT order_payment_id, user_id , MAX(order_id) as lastone
FROM user_orders 
GROUP BY user_id;

but the result is wrong

Answer 1

You can use a self-join to filter out the relevant data

SELECT o1.*
FROM user_orders o1
JOIN
(
   SELECT user_id, MAX(order_created) as lastone 
   FROM user_orders
   GROUP BY user_id
) o2 on o1.user_id = o2.user_id 
    and o1.order_created = o2.lastone
GROUP BY o1.user_id

Answer 2

The MAX should be in the WHERE clause, or it will select the maximum order_id for the whole table.

SELECT order_payment_id, user_id ,order_id as lastone
FROM user_orders u1
WHERE  u1.order_id = (SELECT MAX(order_id)
                      FROM user_orders u2
                      WHERE u1.user_id = u2.user_id);

Using this query, you can get rid of the GROUP BY except if order_id is not unique.

That way you'll get the last order associated with the user.

Answer 3

The general GROUP BY rule is: If a GROUP BY clause is specified, each column reference in the SELECT list must either identify a grouping column or be the argument of a set function.

SELECT order_payment_id, user_id , order_id as lastone
FROM user_orders uo
WHERE order_id = (select MAX(order_id) from user_orders
                  where user_id = uo.user_id)