#语句格式
#CREATE VIEW <视图名>[(<列名>,[,<列名>])]AS<子查询> [WITH CHECK OPTION]

#CREATE VIEW IS_Student
#AS SELECT Sno,Sname,Sage 
#FROM student
#WHERE sdept='is';
#视图没有主码

#基于多个表创建视图

CREATE VIEW IS_S1(Sno,Sname,Grade)
As
SELECT student.Sno,Sname,Grade
FROM student,sc
WHERE sdept='IS'AND
student.Sno=sc.Sno AND
sc.Cno='1';

CREATE VIEW IS_S2
AS 
SELECT Sno,Sname,Grade 
FROM IS_S1
WHERE Grade>=90;

#定义一个反应学生年份的视图
CREATE VIEW BT_S(Sno,Sname,Sbirth)
AS
SELECT Sno,Sname,2014-Sage
FROM student;


#将学生的学号以及平均成绩定义为一个视图
CREATE VIEW S_G(Sno,Gavg)
AS
SELECT Sno,AVG(Grade)
FROM sc
GROUP BY Sno;

#将学生表所有的女生定义为一个视图
CREATE VIEW F_Stuent(F_Sno,F_name,sex,age,dept)
AS
SELECT * 
FROM student
WHERE Ssex='女';

#基本表与视图，mysql删除基本表，有关联视图不会提示