如何双重加入sql查询？

Posted 2023-05-08

【中文标题】如何双重加入sql查询？

【英文标题】：How to double join the sql query?

【发布时间】：2021-10-12 03:37:26

【问题描述】：

我已经构建了这个 sql 查询，它在 phpmyadmin 和 codeigniter 上运行良好；

SELECT teams.team_name,
COUNT(matches.winner) AS win
FROM matches
RIGHT JOIN teams ON teams.team_name = matches.winner
GROUP BY teams.team_name, matches.winner
ORDER BY win DESC

输出：

| team_name    |  win    |
------------------------------
|    India     |    1    |
|    Australia |    4    |
|    England   |    1    |
| South Africa |    0    |

但我需要以下输出：（还有另一列“loser”）因此我需要对“loser”列应用相同的查询，类似于我对“win”列所做的查询。

预期输出：

| team_name    |  win    | loss
------------------------------
|    India     |    1    |  2
|    Australia |    4    |  3
|    England   |    1    |  1
| South Africa |    0    |  2

【问题讨论】：

样本数据和预期结果会有所帮助，请阅读Minimal, Reproducible Example

【参考方案1】：

一种方法是关联子查询：

SELECT t.team_name,
       (SELECT COUNT(*)
        FROM matches m
        WHERE t.team_name = m.winner
       ) as num_wins,
       (SELECT COUNT(*)
        FROM matches m
        WHERE t.team_name = m.loser
       ) as num_loses
FROM matches t
ORDER BY num_wins DESC;