SQL Server基础知识 - where子句

Question

这是我的代码：

use TSQL2012

select 
    emp.empid, emp.firstname, emp.mgrid, 
    manager.firstname as manager_name,
    sum(unique(emp.mgrid)) as Total
from 
    HR.Employees AS emp, HR.Employees as manager
where 
    emp.mgrid = manager.empid
go

我应该得到的结果是：

   empid firstame mgrid manager_name Total
1   2   Don        1    Sara          1
2   3   Judy       2    Don           2
3   4   Yael       3    Judy          2
4   5   Sven       2    Don           2
5   6   Paul       5    Sven
6   7   Russell    5    Sven
7   8   Maria      3    Judy
8   9   Zoya       5    Sven

我无法获得最后一栏（总计）。任何帮助将不胜感激

Answer 1

这样做的一种方法是使用CROSS APPLY：

select emp.empid, emp.firstname, emp.mgrid, manager.firstname as manager_name, 
       x.cnt as Total
from Employees AS emp
inner join Employees as manager on emp.mgrid = manager.empid
cross apply (
   select count(*)
   from Employees AS e
   where e.mgrid = emp.mgrid) AS x(cnt) 

Demo here

修改

您也可以这样使用CTE：

;With C as ( 
   select b.mgrid, count(*) as Total 
   from Employees as b 
   group by mgrid 
) 
select emp.empid, emp.firstname, emp.mgrid, manager.firstname as manager_name, 
       Total 
from Employees AS emp
inner join Employees as manager on emp.mgrid = manager.empid
inner join C on emp.mgrid = C.mgrid

Demo here