[SQL]LeetCode183. 從不訂購的客戶 | 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       |
+-----------+

---

某網站包含兩個表，Customers 表和 Orders 表。編寫一個 SQL 查詢，找出全部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：若是咱們有一個訂購過的客戶列表，很容易知道誰從未訂購過。

咱們能夠使用如下代碼來獲取此類列表。

select customerid from orders;

而後，咱們能夠NOT IN用來查詢不在此列表中的客戶。

1 select customers.name as 'Customers'
2 from customers
3 where customers.id not in
4 (
5     select customerid from orders
6 );

---

222ms

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