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

此题，竟然一时间没想到如何合理的解决方案，主要是有较长的时间没有使用IN与NOT IN.
SQL也是一个手熟的活，需要经常锻炼，以下是解题答案：

# Write your MySQL query statement below
SELECT Customers.Name AS Customers 
FROM Customers
WHERE Customers.Id NOT IN (SELECT CustomerId FROM Orders)

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LeetCode——Customers Who Never Order(灵活使用NOT IN以及IN) Mysql

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