Question

我有三张桌子：
的作用
名字

usr_role
uid，摆脱

USR
uid，用户名，名字

我想加入带有角色表的usr表，并列出第三列中所有用户的所有角色名称，以逗号分隔

例如

uid, username, firstname, roles
1, user1, name1, role_name1, role_name2
2, user2, name2, role_name3, role_name4, role_name 5

我可以通过以下方式加入表：

SELECT DISTINCT u.uid AS userid, u.username AS Username,
                u.firstname AS Name, r.name AS Role 
FROM usr u LEFT JOIN usr_role 
  ON  u.uid=usr_role.uid LEFT JOIN role r 
  ON r.rid=usr_role.rid

但我似乎更进一步

Answer 1

使用GROUP_CONCAT()

SELECT u.uid AS userid, u.username AS Username, u.firstname AS Name, 
       GROUP_CONCAT(r.name) AS Role
  FROM usr u LEFT JOIN usr_role ur
    ON u.uid = ur.uid LEFT JOIN role r
    ON ur.rid = r.rid
 GROUP BY u.uid, u.username, u.firstname

这是SQLFiddle

示例输出：

| userid | Username |      Name |        Role |
|--------|----------|-----------|-------------|
|      1 |     john |      John | role1,role3 |
|      2 |     jane |      Jane |       role2 |

MYSQL：帮助加入三个表

1 个答案: