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 |
+-----------+
select a.Name as Customers
from Customers a
left join Orders b on a.Id=b.CustomerId
where b.CustomerId is null