Question

我有以下查询：

SELECT u.first_name, o.created_at FROM user AS u INNER JOIN order AS o ON o.user_id = u.id GROUP BY u.id

数据结构如下所示：

user 1

order 1 order 2 order 3

user 2

order 1

user 3

order 1 order 2

user 4

order 1 order 2 order 3 order 4 order 5

目前查询返回的数据如下：

user 1 > order 1

user 2 > order 1

user 3 > order 1

user 4 > order 1

但我想拥有用户订单的所有最后一项，如下例所示：

user 1 > order 3

user 2 > order 1

user 3 > order 2

user 4 > order 5

有没有办法很好地解决这个问题？我需要检索每个用户的最后一个订单以生成报告。

Answer 1

尝试此查询： -

SELECT u.first_name, o.created_at
FROM user AS u
INNER JOIN order AS o ON o.user_id =  u.id
Where o.created_at=(SELECT MAX(o2.created_at)
                    FROM order o2
                    WHERE o.user_id =  o2.user_id);
GROUP BY u.id

此SELECT MAX(o2.created_at)用于获取MAX created_at

Answer 2

SELECT u.first_name, max(o.created_at) as max_created_at
FROM user u
INNER JOIN order AS o ON o.user_id =  u.id
GROUP BY u.id

在MySQL中通过desc排序

2 个答案: