MySQL 查询 - 将 3 个表连接在一起，按一列分组并计算其他 2 个表

Question

以下是我正在使用的 3 个表的示例。

    Teams
    +----+------+
    | id | name |
    +----+------+
    |  1 | abc  |
    |  2 | def  |
    |  3 | ghi  |
    +----+------+

    Members
    +----+-----------+----------+---------+
    | id | firstname | lastname | team_id |
    +----+-----------+----------+---------+
    |  1 | joe       | smith    |       1 |
    |  2 | jared     | robinson |       1 |
    |  3 | sarah     | cole     |       3 |
    |  4 | jaci      | meyers   |       2 |
    +----+-----------+----------+---------+

    Goals
    +----+-----------+
    | id | member_id |
    +----+-----------+
    |  1 |         3 |
    |  2 |         2 |
    |  3 |         2 |
    |  4 |         3 |
    |  5 |         1 |
    +----+-----------+
    

我正在尝试获取一个输出类似这样的查询...

    Output
    +--------+----------------+-------------+
    | t.name | Count(members) | Count(goals)|
    +--------+----------------+-------------+
    | abc    |              2 |           3 |
    | def    |              1 |           2 |
    | ghi    |              1 |           0 |
    +--------+----------------+-------------+
    

这是我最接近的结果，但是当我在子查询中使用group by时，我获取“子查询返回多于 1 行”。

select t.name, count(*), 
    (select count(*)
    from teams t 
    inner join members m on m.team_id = t.id
    group by t.id)
from teams t 
inner join members m on m.team_id = t.id 
inner join goals g on g.member_id = m.id
group by t.id

Answer 1

根据我的理解，这是我提出的查询：

    SELECT name, membersCount, IFNULL(totalCount, 0) goalsCount FROM
    (
      SELECT m.team_id, SUM(innerQuery.goalsCount) totalCount
      FROM (
        SELECT m.id memberId, COUNT(*) goalsCount
        FROM Members m
        JOIN Goals g
        ON m.id = g.member_id
        GROUP BY member_id
      ) innerQuery
      JOIN Members m
      ON innerQuery.memberId = m.id
      GROUP BY m.team_id
    ) inner_1
    RIGHT JOIN 
    (
      SELECT t.id, t.name, COUNT(*) membersCount
      FROM Teams t
      JOIN Members m
      ON t.id = m.team_id
      GROUP BY team_id
    ) inner_2
    ON inner_1.team_id = inner_2.id

查询的细分：

#1。获取成员 ID 及其关联的目标计数 (innerQuery)

SELECT m.id memberId, COUNT(*) goalsCount
    FROM Members m
    JOIN Goals g
    ON m.id = g.member_id
    GROUP BY member_id

#2。获取目标总和 (inner_1)

     SELECT m.team_id, SUM(innerQuery.goalsCount) totalCount
      FROM (
          .... Sub-query in step 1
      ) innerQuery
      JOIN Members m
      ON innerQuery.memberId = m.id
      GROUP BY m.team_id

#3 的团队 ID。获取每个团队的总成员数 (inner_2)

    SELECT t.id, t.name, COUNT(*) membersCount
      FROM Teams t
      JOIN Members m
      ON t.id = m.team_id
      GROUP BY team_id

#4。右连接inner_1和inner_2（因为会有NULL）并使用IFNULL检查并替换0

    SELECT name, membersCount, IFNULL(totalCount, 0) goalsCount FROM
    (
     .... Sub-query in step 2
    ) inner_1
    RIGHT JOIN 
    (
      .... Sub-query in step 3
    ) inner_2
    ON inner_1.team_id = inner_2.id