Question

I previously created this SELECT command in SQL Server, that needs to count how many Employees each Department contains. This is what I used:

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

而且它运行良好（即使没有员工，也会向部门显示）。

现在，我想通过以下过滤器只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

But now I get no results. Any idea what I m doing wrong?

Thanks :) Mitsy.

Answer 1

测试字段返回值是否为NULL不是通过相等的=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

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