JOIN 和 GROUP_CONCAT 与三个表

2021-12-17 00:00:00 join sql mysql group-concat

我有三张桌子:

users:        sports:           user_sports:

id | name     id | name         id_user | id_sport | pref
---+--------  ---+------------  --------+----------+------
 1 | Peter     1 | Tennis             1 |        1 |    0
 2 | Alice     2 | Football           1 |        2 |    1
 3 | Bob       3 | Basketball         2 |        3 |    0
                                      3 |        1 |    2
                                      3 |        3 |    1
                                      3 |        2 |    0

表格 user_sports 将 users 和 sports 与偏好顺序 (pref) 联系起来.

The table user_sports links users and sports with an order of preference (pref).

我需要做一个返回这个的查询:

I need to make a query that returns this:

id | name  | sport_ids | sport_names
---+-------+-----------+----------------------------
 1 | Peter | 1,2       | Tennis,Football
 2 | Alice | 3         | Basketball
 3 | Bob   | 2,3,1     | Football,Basketball,Tennis

我尝试过 JOIN 和 GROUP_CONCAT，但结果很奇怪.
我需要进行嵌套查询吗?
有什么想法吗?

I have tried with JOIN and GROUP_CONCAT but I get weird results.
Do I need to do a nested query?
Any ideas?

推荐答案

并不是特别困难.

  1. 使用 JOIN 子句连接三个表.
  2. 在您感兴趣的领域使用 Group_concat.
  3. 不要忘记未连接的字段上的 GROUP BY 子句，否则会发生奇怪的事情


SELECT u.id, 
       u.Name, 
       Group_concat(us.id_sport order by pref) sport_ids, 
       Group_concat(s.name order by pref)      sport_names 
FROM   users u 
       LEFT JOIN User_Sports us 
               ON u.id = us.id_user 
       LEFT  JOIN sports s 
               ON US.id_sport = s.id 
GROUP  BY u.id, 
          u.Name

演示

更新 LEFT JOIN 用于当用户根据评论在 User_Sports 中没有条目时

Update LEFT JOIN for when the user doesn't have entries in User_Sports as per comments

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