LeetCode SQL 570. Managers with at Least 5 Direct Reports 中等

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Table: Employee

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| name        | varchar |
| department  | varchar |
| managerId   | int     |
+-------------+---------+
id is the primary key column for this table.
Each row of this table indicates the name of an employee, their department, and the id of their manager.
If managerId is null, then the employee does not have a manager.
No employee will be the manager of themself.

Write an SQL query to report the managers with at least five direct reports.

Return the result table in any order.

The query result format is in the following example.

Example 1:

Input:
Employee table:
+-----+-------+------------+-----------+
| id  | name  | department | managerId |
+-----+-------+------------+-----------+
| 101 | John  | A          | None      |
| 102 | Dan   | A          | 101       |
| 103 | James | A          | 101       |
| 104 | Amy   | A          | 101       |
| 105 | Anne  | A          | 101       |
| 106 | Ron   | B          | 101       |
+-----+-------+------------+-----------+
Output:
+------+
| name |
+------+
| John |
+------+

题意：编写一个SQL查询，查询至少有5名直接下属的经理 。

---

解法 自连接

完全不用子查询：

select A.name
from Employee A, Employee B
where A.id = B.managerId
group by A.id
having count(*) >= 5;