mysql 2 table with distinct

Question

我有一个像下面这样的查询，我想唯一的输出" "(附上最近的日期)。我该怎么做呢?

select k1.id, k1.username, s1.acctstoptime from radcheck k1 LEFT JOIN radacct s1 ON s1.username=k1.username;

+----+----------+---------------------+
| id | username | acctstoptime        |
+----+----------+---------------------+
|  1 | m        | 2020-10-03 20:00:10 |
|  1 | m        | 2020-10-03 20:00:32 |
|  1 | m        | 2020-10-03 20:12:57 |
|  2 | m1       | NULL                |
|  3 | m3       | NULL                |
|  4 | test123  | NULL                |
|  5 | m01      | NULL                |
|  6 | m00      | NULL                |
|  7 | test123  | NULL                |
|  8 | test     | NULL                |
+----+----------+---------------------+

Answer 1

select MAX(k1.id), k1.username, MAX(s1.acctstoptime) 
from radcheck k1 
LEFT JOIN radacct s1 ON s1.username=k1.username
GROUP BY k1.username;