[SQL]LeetCode183. 从不订购的客户 | Customers Who Never Order

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

---

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

---

方法：使用子查询和NOT IN子句

算法：如果我们有一个订购过的客户列表，很容易知道谁从未订购过。

我们可以使用以下代码来获取此类列表。

select customerid from orders;

然后，我们可以NOT IN用来查询不在此列表中的客户。

select customers.name as 'Customers'
from customers
where customers.id not in
(
    select customerid from orders
);

---

222ms

# Write your MySQL query statement below
SELECT Name as 'Customers' from Customers where Id not in (select CustomerId from Orders)