Database Leetcode Customers Who Never Order

题目：

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       |
+-----------+

题意：

给定两个表Customers和Orders，分别表示的是用户表和订购物品表，要求找出那些没有订购过物品的用户姓名。也就是说，就是找出那些在Customers表中的Id在Orders中没有出现过的用户姓名。考虑用not in来做。

代码如下：

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