Question

我已经研究了这个问题，但我仍然在努力编写一个有效的查询。非常感谢任何帮助。

表

+----------+-------------+
| username | signup_date |
+----------+-------------+
| user1    | 2010-01-15  |
| user1    | 2010-02-15  |
| user2    | 2010-03-15  |
| user3    | 2010-04-15  |
| user3    | 2010-05-15  |
| user4    | 2010-06-15  |
| user5    | 2010-07-15  |
| user6    | 2010-08-15  |
| user6    | 2010-09-15  |
| user6    | 2010-10-15  |
+----------+-------------+

我想编写一个只返回重复的用户名值和最近的signup_date的查询。

期望的结果

+----------+-------------+
| username | signup_date |
+----------+-------------+
| user1    | 2010-02-15  |
| user3    | 2010-05-15  |
| user6    | 2010-10-15  |
+----------+-------------+

到目前为止，我有这个，但它不会过滤到signup_date的最大值。相反，它返回每个重复的行。

SELECT users.username, users.signup_date
FROM users 
INNER JOIN (SELECT username FROM users
GROUP BY username HAVING count(id) > 1) dup ON users.username = dup.username;

Answer 1

这只是一个聚合（不需要连接）：

select u.username, max(u.signup_date)
from users u
group by u.username
having count(*) > 1;

Answer 2

试试这个：

SELECT username, MAX(signup_date)
FROM users
GROUP BY username
HAVING COUNT(username) > 1

选择查询以显示具有最大日期的重复项

2 个答案: