SQL Server SELECT with Count，Group By，Where and Join

Question

我以前在SQL Server中创建了这个SELECT命令，需要统计每个Department包含的雇员人数。 这是我用什么：

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（也显示部，即使有没有员工）。

现在，我想只计算目前正在员工，通过以下过滤器：

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。 任何想法我做错了什么？

谢谢:) Mitsy。

Answer 1

测试，如果现场返回的值是NULL不通过平等=的迹象，但与IS操作

= null 

执行是不行的，而不是写：

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