Solution.sql

/**
 * Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything.
 *
 *  Table: Customers.
 *
 *  +----+-------+
 *  | Id | Name  |
 *  +----+-------+
 *  | 1  | Joe   |
 *  | 2  | Henry |
 *  | 3  | Sam   |
 *  | 4  | Max   |
 *  +----+-------+
 *  Table: Orders.
 *
 *  +----+------------+
 *  | Id | CustomerId |
 *  +----+------------+
 *  | 1  | 3          |
 *  | 2  | 1          |
 *  +----+------------+
 *  Using the above tables as example, return the following:
 *
 *  +-----------+
 *  | Customers |
 *  +-----------+
 *  | Henry     |
 *  | Max       |
 *  +-----------+
 */

select Name as Customers from Customers as c where c.Id not in (select distinct CustomerId from Orders);