SQL刷题求问： Q183. Customers Who Never Order 谢谢

Question

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       |
+-----------+

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/customers-who-never-order
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问题：

请问为啥我使用下面的代码，我可以跑出一模一样的结果，但是提交时候判定我是错的？感谢

SELECT a.Name as Customers
FROM (SELECT Name FROM Customers) AS a
WHERE Name NOT IN (
SELECT c.Name
FROM Customers c INNER JOIN Orders o 
ON c.Id = o.CustomerId)

Answer 1

要用exists语句最方便，我帮你写一个试试看

 

select  name from Customers c where not exists (select CustomerId from Orders where CustomerId = c.id)