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 | +-----------+
解题
select a.Name as 'Customers' from Customers as a left join Orders as b on a.Id=b.CustomerId where b.CustomerId is NULL;
