183. 从不订购的客户

题目链接：https://leetcode.cn/problems/customers-who-never-order/

题目描述：

 

 

我们可以先获得采购的客户名单，然后用NOT IN查询不在列表中的客户：

SELECT customer.name as 'Customers' //注意题目要求返回的列名为Customers

FROM customers

WHERE cunstomers.id NOT IN

(

         SELECT customerid FROM orders

);

第二种解法是使用left join，使用left join连接customers和orders连接条件是 customers.id = orders.customersId and isnull(customersId)。

SELECT customer.name as 'Customers' 
FROM customers
LEFT JOIN orders 
ON customers.id = orders.customerId
WHERE ISNULL(customerId);