mysql - 如何在 MySQL 中以多对多关系在逗号分隔列表中连接来自一个字段的数据？

Question

我在人员和部门之间存在多对多关系，因为一个人可以在多个部门中。

People          Departments
------          -----------
pID  pName      deptID   deptName
1    James      1        Engineering
2    Mary       2        Research
3    Paul       3        Marketing
                4        Communications

People_Departments
------------------
pID   deptID
1     1
1     2
2     2
2     4
3     1
3     2
3     3

我想要的是这样的：

pName  deptName
James  Engineering, Research
Mary   Research, Communication
Paul   Engineering, Research, Marketing

如果我使用下面的 SQL 在表上执行简单的 LEFT JOIN，我将获得与一个人相关的几行：

SELECT people.pName,
       departments.deptName
FROM people
LEFT JOIN people_departments ON people.pID=people_departments.pID
LEFT JOIN departments ON people_departments.deptID=departments.deptID

我尝试了各种组合，GROUP_CONCAT但没有运气。

有什么想法可以分享吗？

Answer 1

    SELECT people.pName,
           GROUP_CONCAT(departments.deptName SEPARATOR ', ') deptName
      FROM people
 LEFT JOIN people_departments 
        ON people.pID = people_departments.pID
 LEFT JOIN departments 
        ON people_departments.deptID = departments.deptID
  GROUP BY people.pID

输出：

+-------+----------------------------------+
| pName | deptName                         |
+-------+----------------------------------+
| James | Engineering, Research            |
| Mary  | Research, Communications         |
| Paul  | Engineering, Research, Marketing |
+-------+----------------------------------+
3 rows in set (0.00 sec)

Answer 2

我的解决方案是：

SELECT people.pName,
GROUP_CONCAT(tmp.deptName SEPARATOR ', ') deptName
FROM people 
LEFT JOIN (SELECT people_departments.pID, departments.deptName FROM people_departments LEFT JOIN departments  ON people_departments.deptID = departments.deptID) as tmp
ON tmp.pID = people.pID
GROUP BY people.pID

结果：

+-------+----------------------------------+
| pName | deptName                         |
+-------+----------------------------------+
| James | Engineering, Research            |
| Mary  | Research, Communications         |
| Paul  | Engineering, Research, Marketing |
+-------+----------------------------------+