570. Managers with at Least 5 Direct Reports

https://leetcode.com/problems/managers-with-at-least-5-direct-reports/description/

SELECT a.name
FROM Employee a
JOIN (
    SELECT managerId
    FROM Employee
    WHERE managerId IS NOT NULL
    GROUP BY managerId
    HAVING COUNT(*) >= 5
) b ON a.id = b.managerId;

Joint 을 이용해서 있는 테이블에서 한번 걸러내주고 답을 구해온다.
MySQL 이든 Oracle 이든 동일.

뭐든간에 속도도 그럭저럭