视图
简化查询语句 简化查询语句，从而使用户避免反复重复的操作 安全性 通过视图用户只能查询和修改他们所见的数据 数据库的其他数据既看不到也取不到 逻辑数据独立性 视图可以帮助用户屏蔽真实表结构变化带来的影响
开始代码
create table a(
aid int primary key,
aname varchar(20)
);
create table b(
bid int primary key,
aid int not null ,
foreign key (aid) references a(aid)
)
##添加几条语句
create or replace view view_aWithB
as select a.*,b.bid from a,b where a.aid=b.aid;
select * from view_aWithB;
insert into view_aWithB(aid,aname) values(3,小兰);
update view_aWithB set aname=李四 where aid=1;
delete from view_aWithB where aid=3;
create or replace view view_b
as select * from b;
delete from view_b where bid=2; ##删除成功
