1. 题目

Customers 表：

+---------------------+---------+
| Column Name         | Type    |
+---------------------+---------+
| customer_id         | int     |
| customer_name       | varchar |
+---------------------+---------+
customer_id 是这张表的主键。
customer_name 是顾客的名称。

Orders 表：

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| order_id      | int     |
| customer_id   | int     |
| product_name  | varchar |
+---------------+---------+
order_id 是这张表的主键。
customer_id 是购买了名为 "product_name" 产品顾客的id。

请你设计 SQL 查询来报告购买了产品 A 和产品 B 却没有购买产品 C 的顾客的 ID 和姓名（ customer_id 和 customer_name ），我们将基于此结果为他们推荐产品 C 。

您返回的查询结果需要按照 customer_id 排序。

查询结果如下例所示。

Customers table:
+-------------+---------------+
| customer_id | customer_name |
+-------------+---------------+
| 1           | Daniel        |
| 2           | Diana         |
| 3           | Elizabeth     |
| 4           | Jhon          |
+-------------+---------------+Orders table:
+------------+--------------+---------------+
| order_id   | customer_id  | product_name  |
+------------+--------------+---------------+
| 10         |     1        |     A         |
| 20         |     1        |     B         |
| 30         |     1        |     D         |
| 40         |     1        |     C         |
| 50         |     2        |     A         |
| 60         |     3        |     A         |
| 70         |     3        |     B         |
| 80         |     3        |     D         |
| 90         |     4        |     C         |
+------------+--------------+---------------+Result table:
+-------------+---------------+
| customer_id | customer_name |
+-------------+---------------+
| 3           | Elizabeth     |
+-------------+---------------+
只有 customer_id 为 3 的顾客购买了产品 A 和产品 B ，却没有购买产品 C 。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/customers-who-bought-products-a-and-b-but-not-c
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

2. 解题

• 注意 having 后面要用聚合函数做判断，不能having(product_name = 'A')

# Write your MySQL query statement below
select customer_id, customer_name
from Customers left join Orders
using(customer_id)
group by customer_id
having sum(product_name = 'A')>0and sum(product_name = 'B')>0and sum(product_name = 'C')=0
order by customer_id

or

# Write your MySQL query statement below
select customer_id, customer_name
from Customers 
wherecustomer_id in (select customer_id from Orders where product_name='A')andcustomer_id in (select customer_id from Orders where product_name='B')andcustomer_id not in (select customer_id from Orders where product_name='C')
order by customer_id

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