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 |
+-----------+
一解
使用左连接（建议）：
SELECT Name as Customers FROM Customers as c LEFT OUTER JOIN Orders as o on c.Id = o.CustomerId WHERE o.Id is NULL
二解
使用 not in（不建议），not in 速度比左连接慢：
SELECT Name as Customers FROM Customers WHERE Id NOT IN (SELECT CustomerId FROM Orders)