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       |+-----------+ 思路一：用IN

1 select Name from Customers where Id not in (select CustomerId from Orders);

思路二：用exists

select Name from Customers c where not exists (select Id from Orders o where c.Id = o.CustomerId);

思路三：用左连接

select Name from Customers c left join Orders o on c.Id = o.CustomerId where o.Id is NULL;