[SQL]LeetCode183. 從不訂購的客戶 | Customers Who Never Order

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
?微信公眾號：山青詠芝（shanqingyongzhi）
?博客園地址：山青詠芝（https://www.cnblogs.com/strengthen/）
?GitHub地址：https://github.com/strengthen/LeetCode
?原文地址：https://www.cnblogs.com/strengthen/p/9720985.html?
?如果鏈接不是山青詠芝的博客園地址，則可能是爬取作者的文章。
?原文已修改更新！強烈建議點擊原文地址閱讀！支持作者！支持原創！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

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

---

某網站包含兩個表，Customers?表和?Orders?表。編寫一個 SQL 查詢，找出所有從不訂購任何東西的客戶。

Customers?表：

+----+-------+
| Id | Name  |
+----+-------+
| 1  | Joe   |
| 2  | Henry |
| 3  | Sam   |
| 4  | Max   |
+----+-------+

Orders?表：

+----+------------+
| Id | CustomerId |
+----+------------+
| 1  | 3          |
| 2  | 1          |
+----+------------+

例如給定上述表格，你的查詢應返回：

+-----------+
| Customers |
+-----------+
| Henry     |
| Max       |
+-----------+

---

方法：使用子查詢和NOT IN子句

算法：如果我們有一個訂購過的客戶列表，很容易知道誰從未訂購過。

我們可以使用以下代碼來獲取此類列表。

select customerid from orders;

然后，我們可以NOT IN用來查詢不在此列表中的客戶。

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)

?