视图是一个虚拟表，是sql的查询结果，其内容由查询定义。同真实的表一样，视图包含一系列带有名称的列和行数据，在使用视图时动态生成。单表视图的数据变化会影响到基表
创建视图:
create view 视图名 as 查询语句
create view newresult
as
select
s.studentName as 姓名, sub.subjectName as 课程, r.examDate as 考试时间, r.studentResult as 成绩
from student s
inner join result r on s.studentNo=r.studentNo
inner join subject sub on r.subjectNo=sub.subjectNo;
select 课程,成绩 from newresult where 成绩>=80; ##视图的使用和表的使用一样
create view newstudent
as
select * from student where studentNo >25;修改视图:
alter view 视图名 as 查询语句
alter view newstudent
as
select * from subject;删除视图:
drop view 视图名;
drop view newstudent;
drop view newresult;