SQL：SELECT COUNT 涉及几个表

Question

我有一个包含四个表的小型 MS Access 数据库，并且正在努力处理涉及所有表的 SELECT COUNT 查询。任何帮助将不胜感激。

数据库概览：

TABLE       COLUMNS

Person         Person_ID |....
Games          Game_ID | Name |....
Played_Games   Played_Games_ID | Game_ID |....
Participation  Played_Games_ID | Person_ID |...

列出所有游戏以及每个游戏总共玩了多少次：

SELECT DISTINCT
Games.Name,
(SELECT COUNT(*) FROM Played_Games WHERE Played_Games.Game_ID = Games.Game_ID) AS TimesPlayed
FROM Games
ORDER BY Games.Name

这很好用，但我还想列出每个游戏由特定群体的成员玩了多少次

我在下面的代码（第 4 行）方面取得了一些进展，但我仍然遇到一个小问题：

在最里面的括号后面对 Games.Game_ID 的引用不再链接到当前的 Game_ID，就像在上面的代码中一样。它现在似乎是未定义的。当我在 MS Access Query Designer 中运行它进行测试时，它要求我输入 Games.Game_ID 的值。如果我然后输入一些随机 Game_ID，代码会“完美”运行，但正如您可能已经发现的那样，TimesPlayedByGroupMembers 的值对于记录集中的每一行都将是相同的，并且仅对我输入的那个特定 Game_ID 为 true

SELECT DISTINCT
Games.Name,
(SELECT COUNT(*) FROM Played_Games WHERE Played_Games.Game_ID = Games.Game_ID) AS TimesPlayed,
(SELECT COUNT(*) FROM (SELECT DISTINCT Played_Games_ID FROM Participation WHERE Played_Games_ID IN (SELECT Played_Games_ID FROM Played_Games WHERE Game_ID = Games.Game_ID) AND Person_ID IN (26, 27, 28))) AS TimesPlayedByGroupMembers
FROM Games
ORDER BY Games.Name

我将尝试从内到外解释我的代码做什么和/或应该做什么

最里面的括号列出了涉及当前游戏的 Played_Games_ID，但这不起作用，因为 Games.Game_ID 未链接到当前 Game_ID

中间的括号（包括上面的那个）列出了涉及当前游戏和一个或多个选定人员的 Played_Games_ID。此处列出的 Person_ID 只是一个示例，这部分代码正在运行

最外面的括号（包括以上所有）计算每个游戏由一个或多个选定的人玩了多少次

我真的很困惑，所以任何帮助都将不胜感激

感谢您的宝贵时间

Answer 1

我的 Access 语法有些生疏，我不能 100% 确定您的表结构，但我认为下面的方法可行。

SELECT  Games.Name, 
        TimesPlayed,
        TimesPlayedByGroupMembers
FROM    Games
        INNER JOIN 
        (   SELECT  Game_ID, 
                    COUNT(*) AS TimesPlayed,
                    SUM(IIF(ISNULL(Participation.Played_Games_ID),0,1)) AS TimesPlayedByGroupMembers
            FROM    Played_Games 
                    LEFT JOIN 
                    (   SELECT  Played_games_ID 
                        FROM    Participation 
                        WHERE   Person_ID IN (1, 2) 
                        GROUP BY Played_games_ID 
                    ) AS Participation 
                        ON Participation.Played_Games_ID = Played_Games.Played_Games_ID
            GROUP BY Game_ID
        ) AS Played_Games
            ON Played_Games.Game_ID = Games.Game_ID
ORDER BY Games.Name

附录：

要让未玩过的游戏显示为 0，请使用以下命令：

SELECT  Games.Name, 
        IIF(ISNULL(TimesPlayed),0,TimesPlayed) AS TimesPlayed,
        IIF(ISNULL(TimesPlayedByGroupMembers),0,TimesPlayedByGroupMembers) AS TimesPlayedByGroupMembers
FROM    Games
        LEFT JOIN 
        (   SELECT  Game_ID, 
                    COUNT(*) AS TimesPlayed,
                    SUM(IIF(ISNULL(Participation.Played_Games_ID),0,1)) AS TimesPlayedByGroupMembers
            FROM    Played_Games 
                    LEFT JOIN 
                    (   SELECT  Played_games_ID 
                        FROM    Participation 
                        WHERE   Person_ID IN (1, 2) 
                        GROUP BY Played_games_ID 
                    ) AS Participation 
                        ON Participation.Played_Games_ID = Played_Games.Played_Games_ID
            GROUP BY Game_ID
        ) AS Played_Games
            ON Played_Games.Game_ID = Games.Game_ID
ORDER BY Games.Name

Answer 2

您的第一个查询通常是这样完成的：

SELECT
Games.Name, COUNT(Played_Games.Game_ID) AS TimesPlayed
FROM Games
INNER JOIN Played_Games ON Played_Games.Game_ID = Games.Game_ID
GROUP BY Games.Name
ORDER BY Games.Name

这可能与您的第二个查询所追求的相近：

SELECT
Games.Name, COUNT(Participation.Played_Games_ID) AS TimesPlayedByGroupMembers
FROM Games
INNER JOIN Played_Games ON Played_Games.Game_ID = Games.Game_ID
INNER JOIN Participation ON Participation.Played_Games_ID = Played_Games.Played_Games_ID
WHERE Participation.Person_ID IN (26, 27, 28)
GROUP BY Games.Name
ORDER BY Games.Name