与3个表相关的SQL计数项

我让sql语句为这两个表运行：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;

然后为系统中的每个线程显示tblThread.Name和TotalStationsInThread

现在，我在这个层次结构中添加了另一个表tblUsers： 每个线程可以有多个用户，每个用户可以有多个站点。 这三个表通过以下方式相互关联：

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

因此，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;

但现在我得到了这样的信息：一个或多个必需参数没有给定值。就像数据库无法通过tblUsers将表tblStations与tblThreads连接一样

关于如何计算连接到每个线程的所有用户的站点数量，请提供任何帮助？？？

您需要在from子句中包含TBluser：

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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;

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非常感谢Gordon Linoff的回答。

不幸的是，这不起作用。它不接受括号中的陈述。@Atlantis。这是一个错误吗？如果是，错误是什么？这是错误：语法错误。在查询表达式“SELECT COUNT*FROM tblUsers JOIN tblStations ON tblStations.fldUserID=tblUsers.fldID WHERE tblUsers.fldThreadID=tblThreads.fldID”中，您使用的是什么SQL引擎？实际上，您应该使用正确的SQL引擎来标记问题。假设表名和字段名存在，我很确定语法是正确的。它可以这样工作：“SELECT tblThreads.*，SELECT COUNTtblStations.fldID FROM tblUsers LEFT OUTER JOIN tblStations ON tblStations.fldUserID=tblUsers.fldID WHERE tblUsers.fldthreaid=tblThreads.fldID AS totalstationsinthreads FROM tblThreads；”但这仅显示一个线程的TotalStationsInThread。

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;