SQL-Customers Who Never Order

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：
way 1：
用嵌套子查询，适合多表格比较的情况。在Customers表中选择Id不在Orders表的CustomerId集合里面的元组
way 2:
用左外连接实现。首先要搞明白普通的连接功能是找到两个表格的公共集合然后形成新的表。

way 1:

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

 way 2:

SQL-Customers Who Never Order

原文：http://www.cnblogs.com/immortal-worm/p/5064726.html