183. 从不订购的客户

1.题目

某网站包含两个表，Customers 表和 Orders 表。编写一个 SQL 查询，找出所有从不订购任何东西的客户。

Customers 表：

+----+-------+
| Id | Name  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+

Orders 表：

+----+------------+
| Id | CustomerId |
+----+------------+
| 1  | 3          |
| 2  | 1          |
+----+------------+

例如给定上述表格，你的查询应返回：

+-----------+
| Customers |
+-----------+
| Henry     |
| Max       |
+-----------+

2.思路

利用not in和子查询：

select Name as 'Customers' from Customers where Id not in(select CustomerId from Orders)

利用左连接：

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