如何为另一个表组合MYSQL Left Join和Group By

SELECT * 
FROM 表1 
LEFT JOIN 表2 
ON 表1.列名 = 表2.列名;

SELECT 列1, 列2, ... 
FROM 表 
GROUP BY 列1, 列2, ...;

+----+----------+
| id | username |
+----+----------+
|  1 | John     |
|  2 | Lisa     |
|  3 | Mike     |
+----+----------+

+---------+--------+
| user_id | amount |
+---------+--------+
|       1 |  100.0 |
|       1 |   50.0 |
|       2 |   75.0 |
|       3 |   25.0 |
+---------+--------+

+----------+---------+--------+
| username | user_id | amount |
+----------+---------+--------+
| John     |       1 |  150.0 |
| Lisa     |       2 |   75.0 |
| Mike     |       3 |   25.0 |
+----------+---------+--------+

SELECT A.username, B.user_id, SUM(B.amount) as amount
FROM 用户表 A
LEFT JOIN 订单表 B ON A.id = B.user_id
GROUP BY A.username, B.user_id;