mysql - 连接多对多并将许多引用合并到单行中

Question

我咨询过类似的问题，但问题不同，因为我不仅有多对多的联接，而且还有一对多的联接。

用户

+----+-------+---------------+
| id | first | department_id |
+----+-------+---------------+
|  1 | John  | 1             |
|  2 | Jane  | 2             |
+----+-------+---------------+

部门

+----+------------+
| id |   name     |
+----+------------+
|  1 | purchasing |
|  2 | HR         |
|  3 | marketing  |
+----+------------+

角色

+----+----------+
| id |   name   |
+----+----------+
|  1 | admin    |
|  2 | accounts |
|  3 | sales    |
+----+----------+

用户角色

+--------+----------+
| user_id | role_id |
+--------+----------+
|      1  |       1 |
|      1  |       2 |
|      1  |       3 |
|      2  |       2 |
|      2  |       3 |
+--------+----------+

sql

SELECT user.first, GROUP_CONCAT(role.name), department.id AS 'department.id', department.name AS 'department.name'
FROM user 
INNER JOIN department ON user.department_id
INNER JOIN user_role ON user.id = user_role.user_id
INNER JOIN role ON user_role.role_id = role.id
GROUP BY user.name;

期望

John, "admin,accounts,sales", 1, purchasing
Jane, "accounts,sales", 2, HR

本质上它是一个 4 表连接，具有多对多和一对多的组连接功能。

查询出错。

Error Code: 1055. Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'department.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

Answer 1

由于每个用户的部门都是唯一的，因此您可以使用 max() 获取部门详细信息，以克服 group by 带来的限制。

SELECT 
  user.first, 
  GROUP_CONCAT(role.name) AS roles, 
  max(department.id) AS department_id, 
  max(department.name) AS department_name
FROM user 
INNER JOIN department ON user.department_id = department.id
INNER JOIN user_role ON user.id = user_role.user_id
INNER JOIN role ON user_role.role_id = role.id
GROUP BY user.first;

此外，如果用户名不唯一，您应该:

GROUP BY user.id, user.first

此外，列的别名不得用单引号括起来。请改用反引号。