如何在MySQL中以多对多关系从逗号分隔列表中的一个字段连接数据？

• Z时代
• 2024-01-10
• 分类：问答

我和人与部门之间存在多对多关系，因为一个人可以在许多部门中工作。

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：

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

如果我使用下面的SQL在表上进行普通的LEFT JOIN连接，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

我尝试过各种组合，GROUP_CONCAT但没有运气。

有什么想法要分享吗？

回答：

    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)

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