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 。
解题
select c.customer_id, c.customer_name from Customers as c left join Orders as o on c.customer_id=o.customer_id group by o.customer_id having count(if(o.product_name='A',1,null))>0 and count(if(o.product_name='B',1,null))>0 and count(if(o.product_name='C',1,null))=0;
