数据库实验—视图定义与操作

create view V_IS 
as 
select Sno, Sname, Sage from S where Sdept = 'IS';

create view V_S_C_G 
ss select S.Sno, Sname, C.Cno, Cname, Grade
from S, C,SC where S.Sno = SC.Sno and C.Cno = SC.Cno;

create view V_NUM_AVG
as select count(Sno) as NUM, avg(Sage) as AVG
from S group by Sdept;

create view V_YEAR 
as select (2020 – Sage) as YEAR from S;

create view V_AVG_S_G
as 
select count(Cno) as NUM, avg(Grade) as AVG
from SC group by Sno;

create view V_AVG_C_G
as 
select Cno,count(Sno) as NUM,avg(Grade) as AVG
from SC group by Cno;

select Sno,Sname, Grade from V_S_C_G 
where Sno in 
select Sno from V_S_C_G 
group by Sno 
having avg(Grade) >=90;

select * from V_S_C_G
where Sno in 
(select X.Sno from V_S_C_G X
where not exists
(select Y.Grade from V_S_C_G Y
where Grade <=
(select avg(Grade) from V_S_C_G Z 
where (Y.Cno = Z.Cno) and (X.Sno = Y.Sno)))); 

select Sdept,count(Sno) as NUM. from S
where Sno in 
(select V_S_C_G.Sno from V_S_C_G 
group by V_S_C_G.Sno 
having avg(Grade)>=80) 
group by Sdept;

update V_IS set Sname = ‘周芷若’ where Sno = ‘1’;

update V_Is set Sname = ‘乔峰’ where Sno = ‘4’;

select * from S;

insert into V_IS(Sno ,Sname, Sage,Sdept) values
('S12', 'YAN XI', 19. 'IS')

insert into V_IS(Sno, Sname, Sage, Sdept)values
('10','木婉清',19,'IS');

select * from S;

delete from V_IS 
where Sno = ‘s12’ or Sno = ‘S3’

可以；
update V_SC_G set Sname = ‘S12_MMM’ 
where Sno = ‘S12’；