[LeetCode] Customers Who Never Order

https://leetcode.com/problems/customers-who-never-order/

Customers Who Never Order - LeetCode

상품을 주문한 적 없는 회원을 찾는 문제

 

나의 풀이 - Left Join 활용

SELECT
    Customers
FROM
    (SELECT 
        name AS Customers, customerId
    FROM Customers AS c LEFT JOIN Orders AS o
    ON c.id = o.customerId
    ) AS m
WHERE customerId is NULL
;

----------------------------------------------
SELECT 
    Name AS 'Customers'
FROM Customers c LEFT JOIN Orders o
    ON c.Id = o.CustomerId
WHERE o.CustomerId IS NULL
;

 

다른 풀이 - 서브쿼리 활용

select customers.name as 'Customers'
from customers
where customers.id not in
(
    select customerid from orders
);

속도는 두 방법 거의 동일했다.