문제
Leetcode - 183. Customers Who Never Order
Table: Customers
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| id | int |
| name | varchar |
+-------------+---------+
id is the primary key (column with unique values) for this table.
Each row of this table indicates the ID and name of a customer.
Table: Orders
+-------------+------+
| Column Name | Type |
+-------------+------+
| id | int |
| customerId | int |
+-------------+------+
id is the primary key (column with unique values) for this table.
customerId is a foreign key (reference columns) of the ID from the Customers table.
Each row of this table indicates the ID of an order and the ID of the customer who ordered it.
Write a solution to find all customers who never order anything.
Return the result table in any order.
The result format is in the following example.
풀이
나의 풀이
SELECT c.name AS Customers
FROM customers c
LEFT JOIN orders o ON c.id = o.customerId
WHERE o.id IS NULL다른 사람 풀이
SELECT name as Customers
from Customers
where id not in (
select customerId
from Orders배운점
- orders 테이블에 주문 아이디가 없는 사람이 한번도 주문하지 않은 사람이라는 idea로 풀기. -> WHERE 서브쿼리 활용
