[Leetcode, PostgreSQL] 183. Customers Who Never Order

문제

• Write a solution to find all customers who never order anything.

• Example:

    Input: 
    Customers table:
    +----+-------+
    | id | name  |
    +----+-------+
    | 1  | Joe   |
    | 2  | Henry |
    | 3  | Sam   |
    | 4  | Max   |
    +----+-------+
  
    Orders table:
    +----+------------+
    | id | customerId |
    +----+------------+
    | 1  | 3          |
    | 2  | 1          |
    +----+------------+
  
    Output: 
    +-----------+
    | Customers |
    +-----------+
    | Henry     |
    | Max       |
    +-----------+
  

코드

SELECT CUST.NAME as Customers
FROM CUSTOMERS CUST
WHERE NOT EXISTS (SELECT CUSTOMERID FROM ORDERS ORD WHERE CUST.ID = ORD.CUSTOMERID)
;