MySQL视图

视图是一种为了安全考虑的策略，对于部分字段不想被看到，就在视图中去掉这个字段。

 

视图的特点：

 

视图的列可以来自不同的表

视图是基本表的抽象

视图的建立和删除不影响原表

视图内容更新影响原表

当视图来自多个表的时候，不允许添加、删除数据。

 

创建视图

 

create view viewname as 查询语句;

 

操作视图和操作表一样

 

 

创建常量视图

 

create view view name as select 3.1415926;

 

创建聚合函数的视图

 

create view viewname as select count(name) from t_student;

 

创建带有排序功能的查询视图

 

create view viewname as select name from t_student order by id desc;

 

创建带有内连接查询的视图

 

create view viewname as select s.name from t_student as s, t_group as g where s.group_id = g.id and g.id =2;

创建带有外联接的视图

 

create view viewname as select s.name from t_student as s left join t_group as g on s.group_id = g.id where g.id =2;

 

创建带有子查询相关的视图

 

create view viewname as select s.name from t_student as s where group_id in (select id from t_group);

 

创建union的视图

 

create view viewname as select id,name from t_student union all select id,name from t_group;

 

删除视图

 

drop view viewname

 

替换视图

 

create or replace view viewname as 查询语句;

 

修改视图

 

alter view viewname as 新的查询;

 

查询视图数据

 

select * from viewname;

 

添加数据

 

insert into viewname(column,···) values(val,···);

 

更新数据

 

update viewname set column = val where ···

 

删除数据

 

delete from viewname where ···

 

标签：viewname,create,视图,MySQL,id,select,view
来源： https://blog.csdn.net/Day_and_Night_2017/article/details/96156947