Question

我为这两个表运行了这个sql语句：tblStations和tblThreads，用于计算每个线程中的站数：

SELECT tblThreads.*, (SELECT COUNT(*) FROM tblStations WHERE tblStations .fldThreadID=tblThreads.fldID) AS TotalStationsInThread FROM tblThreads;

然后显示系统中每个线程的tblThread.Name和TotalStationsInThread。

现在我在此层次结构中添加了另一个表（tblUsers）：每个线程可以有很多用户，每个用户可以拥有多个站点。这三个表格相互关联：

tblStations.fldUserID=tblUsers.fldID > tblUsers.fldThreadID=tblThreads.fldID.

所以我将SQL查询更改为：

SELECT tblThreads.*, (SELECT COUNT(*) FROM tblStations WHERE tblStations.fldUserID=tblUsers.fldID AND tblUsers.fldThreadID=tblThreads.fldID) AS TotalStationsInThread FROM tblThreads;

但是现在我收到了这样的信息：“没有给出一个或多个必需参数的值。”这就像数据库无法通过tblUsers将表tblStations与tblThreads连接起来......

有关如何计算连接到每个线程的所有用户的站点数量的任何帮助吗？

Answer 1

这是MS Access Jet数据库引擎的正确答案：

SELECT tblThreads.*, (SELECT COUNT(tblStations.fldUserID) FROM tblStations INNER JOIN tblUsers ON tblStations.fldUserID = tblUsers.fldID WHERE  tblUsers.fldThreadID = tblThreads.fldID)  AS TotalStationsInThread FROM tblThreads;

非常感谢Gordon Linoff的回答。

Answer 2

您需要在tblUsers子句中加入from：

SELECT tblThreads.*,
       (SELECT COUNT(*)
        FROM tblUsers inner join
             tblStations
             on tblStations.fldUserID = tblUsers.fldID
        WHERE tblUsers.fldThreadID = tblThreads.fldID
       ) AS TotalStationsInThread
FROM tblThreads;

与3个表相关的SQL COUNT条目

2 个答案: