LeetCode：Database 14.至少有5名直接下属的经理

Posted 2021-05-16 Xiao Miao

要求：给定 Employee 表，请编写一个SQL查询来查找至少有5名直接下属的经理的姓名。

Employee 表：

+------+----------+-----------+----------+
|Id    |Name 	  |Department |ManagerId |
+------+----------+-----------+----------+
|101   |John 	  |A 	      |null      |
|102   |Dan 	  |A 	      |101       |
|103   |James 	  |A 	      |101       |
|104   |Amy 	  |A 	      |101       |
|105   |Anne 	  |A 	      |101       |
|106   |Ron 	  |B 	      |101       |
+------+----------+-----------+----------+
Employee 表包含所有员工和他们的经理。每个员工都有一个 Id，并且还有一列是经理的 Id

Result Table：

+-------+
| Name  |
+-------+
| John  |
+-------+

分析：
1.通过经理id分组，找出大于五个直接下属的经理id
2.通过经理id找到经理姓名

#1.方法1
select a.Name from
Employee a
join
Employee b
on a.Id=b.ManagerId
group by b.ManagerId
having count(b.ManagerId)>=5
#2.方法2
select Name from
Employee 
where Id in(select ManagerId from 
Employee 
group by ManagerId
having count(ManagerId)>=5)