存储过程以查找过去n个月中雇用的员工数量

Question

我正在尝试创建一个存储过程，该过程返回Northwind数据库中最近n个月雇佣的员工数。这就是我得到的：

CREATE PROC spGetEmployeeCountByDateHire
@num1 int 
,@num2 int 
,@EmployeeCount int output
 WITH Encryption 
AS 
BEGIN 
select @EmployeeCount = COUNT(*),
DATEDIFF(DAY, HireDate, getdate()) AS Diff 
FROM  Employees where DATEDIFF(DAY, HireDate, getdate()) between @num1 and @num2 
ORDER BY HireDate Desc END

我得到了这个错误：消息141，级别15，状态1，过程spGetEmployeeCountByDateHire，第8行为变量赋值的SELECT语句不能与数据检索操作结合使用。

有人可以帮我理解我做错了吗？

Answer 1

错误正是告诉您不能将count(*)分配给变量并同时选择datediff操作的原因。通过从选择列表

中删除DATEDIFF(DAY, HireDate, getdate()) AS Diff部分，更改您的选择语句，如下所示

select @EmployeeCount = COUNT(*)
FROM  Employees 
where DATEDIFF(DAY, HireDate, getdate()) between @num1 and @num2