sql-server-2008 - 带有计数、分组依据、位置和连接的 SQL Server SELECT

Question

我之前在 SQL Server 中创建了这个 SELECT 命令，它需要计算每个部门包含多少员工。这是我使用的：

SELECT Departments.Description AS [Department], COUNT(Employees.ID) AS [Employees]
FROM Employees 
RIGHT JOIN Departments ON
Employees.DepartmentID = Departments.ID 
GROUP BY Departments.Description

它工作正常（即使没有员工，也显示部门）。

现在，我只想通过以下过滤器计算当前工作的员工：

WHERE Employees.JobEndDate = null

我试着这样做：

SELECT   Departments.Description AS [Department], COUNT(Employees.ID) AS [Employees] 
FROM Employees 
RIGHT JOIN Departments ON
Employees.DepartmentID = Departments.ID 
WHERE Employees.JobEndDate = NULL 
GROUP BY Departments.Description

但现在我没有得到任何结果。知道我做错了什么吗？

谢谢 :) 米西。

Answer 1

测试字段返回值是否NULL不是通过=等号而是通过IS运算符执行的

= null

不起作用，而是写：

Employees.JobEndDate IS NULL

Answer 2

SELECT Departments.Description AS [Department], COUNT(Employees.ID) AS [Employees] FROM Employees RIGHT JOIN Departments ON Employees.DepartmentID = Departments.ID WHERE Employees.JobEndDate = IS NULL GROUP BY Departments.Description