183. 从不订购的客户

题目描述

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

分析

通过左连接实现，where 筛选 CustomerId is null的数据

代码

# Write your MySQL query statement below
select a.Name as Customers 
    from Customers a left join Orders b on a.Id = b.CustomerId 
        where b.CustomerId is null; 

题目链接

https://leetcode-cn.com/problems/customers-who-never-order/description/