发布时间 : 星期一 文章数据库实验四答案更新完毕开始阅读
数据库实验四答案
--实验四--
--1. 定义“IS”系学生基本情况视图V_IS 并查询结果; create view V_IS as
select * from S
where Sdept='IS' with check option;
select * from V_IS;
--2. 将S,C,SC表中学生的学号,姓名,课程号,课程名,成绩定义为视图V_S_C_G并查询结果; create view V_S_C_G as
select S.Sno,Sname,C.Cno,Cname from S,C,SC
where S.Sno=SC.Sno and C.Cno=SC.Cno;
select *
from V_S_C_G;
--3. 将各系学生人数,平均年龄定义为视图V_NUM_AVG并查询结果; create view V_NUM_AVG as
select count(Sno) DeptNum ,avg(Sage) DeptAvgAge,Sdept from S
group by Sdept;
select *
from V_NUM_AVG;
--4. 定义一个反映学生出生年份的视图V_YEAR并查询结果; create view V_YEAR as
select Sno,2012-Sage birthday from S;
select *
from V_YEAR;
--5. 将各位学生选修课程的门数及平均成绩定义为视图V_AVG_S_G并查询结果;
create view V_AVG_S_G as
select SC.Sno,count(SC.Cno) CountCno,avg(Grade) AvgGrade from S,C,SC
where S.Sno=SC.Sno and C.Cno=SC.Cno group by SC.Sno;
select *
from V_AVG_S_G;
--6. 将各门课程的选修人数及平均成绩定义为视图V_AVG_C_G并查询结果; create view V_AVG_C_G as
select count(SC.Sno) Cnum,avg(Grade) AvgGrade from S,C,SC
where S.Sno=SC.Sno and C.Cno=SC.Cno group by SC.Cno;
select *
from V_AVG_C_G;
--7. 查询平均成绩为90分以上的学生学号、姓名和成绩; select SC.Sno,Sname,avg(Grade) AvgGrade from S,SC
where S.Sno=SC.Sno group by SC.Sno,Sname having avg(Grade) >90;
--8. 查询各课成绩均大于平均成绩的学生学号、姓名、课程和成绩; create view V_AVG as
select SC.Cno,avg(Grade) AvgGrade from C,SC
where C.Cno=SC.Cno group by SC.Cno;
select
distinct S.Sno,Sname,C.Cno,Grade
from S,SC,C,V_AVG
where S.Sno=SC.Sno and C.Cno=V_AVG.Cno and Grade >V_AVG.AvgGrade ;
--9. 按系统计各系平均成绩在80分以上的人数,结果按降序排列; select Sdept,count(AvgGrade) Num from S,V_AVG_S_G
where S.Sno=V_AVG_S_G.Sno and AvgGrade > 80 group by Sdept order by Num desc;
--10 通过视图V_IS,分别将学号为“S1”和“S4”的学生姓名更改为“S1_MMM”,”S4_MMM” 并查询结果;
insert into S(Sno,Sname,Ssex,Sage,Sdept) values('200215121','三毛','男',21,'IS');
insert into S(Sno,Sname,Ssex,Sage,Sdept) values('200215124','紫薇','女',19,'IS');
update V_IS set Sno='S1_MMM' where Sno='200215121'; update V_IS set Sno='S4_MMM' where Sno='200215124';
select * from V_IS;
--11. 通过视图V_IS,新增加一个学生记录 ('S12','YAN XI',19,'IS'),并查询结果; insert into V_IS(Sno,Sname,Sage,Sdept) values('S12','YAN XI',19,'IS');
select * from V_IS
where Sno='S12';
--11. 通过视图V_IS,新增加一个学生记录 ('S13','YAN XI',19,'MA'),并查询结果;
insert into V_IS(Sno,Sname,Sage,Sdept) values('S13','Y
AN XI',19,'MA');
-- Tip:由于该学生是MA系的,当有check约束时将会产生更新错误。
--13. 通过视图V_IS,删除学号为“S12”和“S3”的学生信息,并查询结果; insert into V_IS(Sno,Sname,Sage,Sdept) values('S3','李杨',21,'IS');
select * from V_IS;
delete from V_IS
where Sno='S12';
delete from V_IS
where Sno='S3';
select * from V_IS;
--14. 要通过视图V_S_C_G,将学号为“S12”的姓名改为“S12_MMM”,是否可以实现?
update V_S_C_G
set Sname='S12_MMM' where Sno='S12';
--15. 要通过视图V_AVG_S_G,将学号为“S1”的平均成绩改为90分,是否可以实现?
-- 不能实现,因为视图不是真正存在的,对视图的修改实际上是对基本表的修改, -- 而平均分在基本表中不存在,涉及到多个成绩,所以不能修改。