在SQL中显示员工姓名(Boss)和员工(下属)的数量

Question

我有一个表emp有foll数据:

EmpID    EmpName   MgrID 

100     King        NULL
101     Smith       100
102     Shine       100
103     Racy        102

现在我想显示员工姓名(Boss)和员工(下属)的数量

BOSS       SUBORDINATES

---

BLAKE                 5

CLARK                 1

FORD                  1

JONES                 2

KING                  3

SCOTT                 1

请指导如何在SQL Server 2008中查询此表.

尝试查询:

select e.first_name as ename,m.first_name as mname from employees e,employees m where e.manager_id=m.employee_id

Answer 1

• 从自我加入开始 EmpID=MgrID
• 分组MgrID和EmpName
• 选择EmpName和count(*)

将其转换为SQL是机械的:

SELECT b.EmpName, COUNT(*)
FROM Employee e
JOIN Employee b ON b.EmpID=e.MgrID
GROUP BY b.EmpID, b.EmpName