题175. 组合两个表 (左连接)
思路:左连接left join , 右表是可能地址为空的address表。
select p.firstname,p.lastname,a.city,a.state from person as p left join address as a on p.personid=a.personid
题183. 从不订购的客户:(左连接的过滤)
思路:通过左连接显示所有客户的订单,没有订购任何东西的orders表id为null
select name as customers from customers as c left join orders as o on c.id=o.customerid where o.id is null;
如对本文有疑问, 点击进行留言回复!!
网友评论