mysql - 显示监管 3 名或更多员工的主管

Question

员工表

ID    Name        Supervisor_ID

1     James        NULL
2     Peter        1
3     Howard       1
4     Michele      2
5     Nicholas     2
6     Donald       2
7     Jackson      3
8     Anderson     3
9     Jeff         3
10    Will         3

我应该在最后得到这个

ID    Name     Supervisor_Of_X_Employee

4     Peter    3
2     Howard   4

我试过

SELECT t1.employee_id
FROM  employee t1
      JOIN (SELECT DISTINCT supervisor_id FROM employee) t2
      ON t1.employee_id = t2.supervisor_id; 

似乎没有产生我想要的东西

有什么想法吗？

谢谢

Answer 1

你想找到主管人数，所以你像这样对主管 ID 进行分组

SELECT Supervisor_ID, count(*) as CNT
FROM  employee
GROUP BY Supervisor_ID

添加 HAVING COUNT(*) > 2 以获得 3 或更多的数。

哦...但你也想要这个名字？然后你必须重新加入表以获取名称。

SELECT E.ID, E.Name, SUB.CNT 
FROM (
  SELECT Supervisor_ID, count(*) as CNT
  FROM  employee
  GROUP BY Supervisor_ID
  HAVING COUNT(*) > 2
) AS SUB
JOIN employee as E on E.ID = SUB.Supervisor_ID