--创建视图
/*
create view empview2
as
select employee_id,last_name,salary from employees where department_id = 80
*/

--修改视图
/*
create or replace view empview2
as
select employee_id,salary from employees where department_id = 80
*/

--创建复杂视图
/*
create or replace view empview3
as
select department_name,avg(salary) avg_sal from employees e,departments d
where e.department_id = d.department_id group by department_name
*/

--删除视图
drop view empview3


--屏蔽视图的DML操作
/*
create view empview4
as
select employee_id,salary from employees where department_id = 80
with read only
*/

--对视图数据进行修改和删除
update empview4 set salary = 1200 where employee_id = 179;
delete from empview4 where employee_id = 179;

PS：视图中使用DML的规定

1.当视图定义中包含以下元素之一时不能使用insert：

组函数；group by 子句；distinct 关键字；rownum 伪列；列的定义为表达式；表中非空的列在视图定义中未包括。

2.当视图定义中包含以下元素之一时不能使用update：

group by 子句；distinct 关键字；rownum伪列；列的定义为表达式；

3.当视图定义中包含以下元素之一时不能使用update：

组函数；group by 子句；distinct 关键字；rownum 伪列。