mysql - 如何连接多个表，包括查找表并按行返回数据

Question

我正在尝试显示一些简单的计算机游戏结果，并使其易于在我的代码中逐行遍历结果。我想要它，以便每场比赛的所有相关数据都在每条记录中，这样我就可以在一行上输出所有数据，例如：

• A队（45分）vs B队（55分），比赛时长：5分钟
• C队（60分）vs D队（65分），比赛时长：4.3分钟

因此，对于一场比赛，有两支球队互相比赛，他们各自在比赛结束时得分。基本上，每场比赛的 games_teams 表中最终都会有两行。

这是我的架构：

这是我的表格数据：

这是我想要实现的输出，因此我可以轻松地遍历结果并将它们输出到页面上：

我设法通过一些可怕的 SQL 和许多子查询来实现这一点，如下所示：

SELECT games.game_id, game_name, game_duration, 
(SELECT team_id FROM games_teams WHERE games.game_id = games_teams.game_id LIMIT 0, 1) AS team_id_a,
(SELECT team_id FROM games_teams WHERE games.game_id = games_teams.game_id LIMIT 1, 1) AS team_id_b,
(SELECT teams.team_name FROM games_teams INNER JOIN teams ON games_teams.team_id = teams.team_id WHERE games.game_id = game_id LIMIT 0, 1) AS team_name_a,
(SELECT teams.team_name FROM games_teams INNER JOIN teams ON games_teams.team_id = teams.team_id WHERE games.game_id = game_id LIMIT 1, 1) AS team_name_b,
(SELECT team_score FROM games_teams WHERE games.game_id = games_teams.game_id LIMIT 0, 1) AS team_score_a,
(SELECT team_score FROM games_teams WHERE games.game_id = games_teams.game_id LIMIT 1, 1) AS team_score_b
FROM games

该方法的问题是它会很慢并且无法扩展。我还需要从 games_teams 表中提取其他游戏统计信息，这样就会有更多的子查询。

我尝试的另一种方法是：

我通过以下 SQL 实现了这一点：

SELECT games.game_id, game_name, game_duration, teams.team_id, team_name, team_score
FROM games
INNER JOIN games_teams ON games.game_id = games_teams.game_id
INNER JOIN teams ON games_teams.team_id = teams.team_id

现在这种方式将更难在代码中遍历，因为每个游戏的相关数据都在两个不同的记录中。我必须构建该行的第一部分，然后进入下一个循环迭代并打印下一部分。然后为下一场比赛重新开始，我试图在一行上显示所有信息，例如：

A队（45分）vs B队（55分），比赛时间：5分钟

所以这就是为什么我认为如果全部都在一张唱片上会更容易。有没有办法很好地完成这一点，所以如果我需要 games_teams 表中的更多列，它也可以扩展？

如果您需要重新创建它，这是一个包含数据库代码的 pastebin 链接。

非常感谢任何帮助，谢谢！

Answer 1

您需要加入 games_teams 和团队两次，例如：

SELECT ga.game_id
        , ga.game_name
        , ga.game_duration
        , t1.team_name, gt1.team_score
        , t2.team_name, gt2.team_score
FROM games ga
JOIN games_teams  gt1 ON gt1.game_id = ga.game_id
JOIN games_teams  gt2 ON gt2.game_id = ga.game_id
JOIN teams t1 ON t1.team_id = gt1.team_id
JOIN teams t2 ON t2.team_id = gt2.team_id
WHERE gt1.team_id < gt2.team_id
        ;

挤出 {games_teams * teams} 子连接并引用它两次的干净方法是将其放入 CTE 中：（不幸的是 mysql 不支持 CTE）

WITH gtx AS (
        SELECT gt.game_id
        , gt.team_score
        , te.team_id
        , te.team_name
        FROM games_teams gt
        JOIN teams te ON te.team_id = gt.team_id
        )
SELECT ga.game_id 
        , ga.game_name
        , ga.game_duration
        , g1.team_name, g1.team_score
        , g2.team_name, g2.team_score
FROM games ga
JOIN gtx g1 ON g1.game_id = ga.game_id
JOIN gtx g2 ON g2.game_id = ga.game_id
WHERE g1.team_id < g2.team_id
  ;

结果：

 game_id | game_name | game_duration | team_name | team_score | team_name | team_score 
---------+-----------+---------------+-----------+------------+-----------+------------
       1 | Game A    |           300 | Team A    |         45 | Team B    |         55
       2 | Game B    |           258 | Team C    |         60 | Team D    |         65
(2 rows)

Answer 2

由于每场比赛总是有两支球队，因此您可以使用 UNION 来获取每场比赛的球队，这简化了这一点，如下所示：

SELECT q2.game_id, games.game_name, games.game_duration,
       q2.team_id_a, q2.team_id_b,
       teams_a.team_name AS team_name_a,
       teams_b.team_name AS team_name_b,
       games_teams_a.team_score AS team_score_a,
       games_teams_b.team_score AS team_score_b
FROM  (SELECT q.game_id,
              MAX(q.team_id_a) AS team_id_a,
              MAX(q.team_id_b) AS team_id_b
          FROM (
               SELECT games_teams.game_id,
                      MIN(games_teams.team_id) AS team_id_a,
                      0 AS team_id_b
               FROM   games_teams
               GROUP BY games_teams.game_id
            UNION
               SELECT games_teams.game_id,
                      0 AS team_id_a,
                      MAX(games_teams.team_id) AS team_id_b
               FROM   games_teams
               GROUP BY games_teams.game_id
         ) q
        GROUP BY q.game_id) q2
   INNER JOIN games ON q2.game_id = games.game_id
   INNER JOIN teams teams_a ON q2.team_id_a = teams_a.team_id
   INNER JOIN teams teams_b ON q2.team_id_b = teams_b.team_id
   INNER JOIN games_teams games_teams_a ON
              q2.game_id = games_teams_a.game_id AND q2.team_id_a = games_teams_a.team_id
   INNER JOIN games_teams games_teams_b ON
              q2.game_id = games_teams_b.game_id AND q2.team_id_b = games_teams_b.team_id;