Question

我以前在SQL Server中创建了这个SELECT命令，需要计算每个Department包含的Employees数量。这是我用过的：

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，我想通过以下过滤器只计算当前正在工作的员工：

WHERE Employees.JobEndDate = null

我试过这样做：

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

但现在我没有结果。知道我做错了吗？

谢谢:) Mitsy。

Answer 1

测试字段返回值是NULL是否不是通过相等的=符号执行，而是IS运算符

= 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

带有Count，Group By，Where和Join的SQL Server SELECT

2 个答案: