[LeetCode/MySQL]584. Find Customer Referee

문제

Find Customer Referee

문제 풀이

1. 기본 WHERE

SELECT name
FROM Customer
WHERE referee_id!=2 OR referee_id IS NULL;

2. LEFT JOIN

SELECT c1.name
FROM Customer c1
LEFT JOIN Customer c2
ON c1.referee_id=c2.id AND c2.id=2
WHERE c2.id IS NULL;

3. 서브쿼리

SELECT name
FROM Customer
WHERE id NOT IN (
    SELECT id
    FROM Customer
    WHERE referee_id = 2
);