LeetCode -183-数据库- 从不订购的客户

问题描述：

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

1、使用 not in

#使用 not in
SELECT c.Name as Customers from Customers c
where c.Id not in 
(select distinct o.CustomerId Id from orders o );

2、使用  not exists 

SELECT c.Name as Customers from Customer c
where not exists
(select distinct o.CustomersId Id from order o where c.Id = o.CustomerId);

3、使用左连接  深入理解SQL的四种连接-左外连接、右外连接、内连接、全连接

select c.Name as Customers from Customers c 

left join Orders o on c.Id = o.CustomerId

where o.CustomerId  is null;