SQL 连接(JOIN)

SQL 连接(JOIN) https://www.runoob.com/sql/sql-join.html

select *from Users u left join Classes c on u.id=c.userid 

select *from Users u right join Classes c on u.id=c.userid 

select *from Users u join Classes c on u.id=c.userid

select *from Users u left join Classes c on u.id=c.userid where c.userid is null

select *from Users u right join Classes c on u.id=c.userid where u.id is null

select *from Users u full outer join Classes c on u.id=c.userid

select *from Users u full outer join Classes c on u.id=c.userid where c.userid is null or u.id is null

posted @ 2019-12-26 17:32  Challenge-Yourself  阅读(157)  评论(0)  编辑  收藏  举报