SQL语句（十七）综合练习_分组查询_内嵌查询_视图使用

Select * from Student
Select * From Course
Select * from SC

--子查询  低于总平均成绩的女同学成绩
Select Grade
from Student, SC
Where Student.Sno = SC.Sno and Student.Sex = '女' and 
      Grade < (Select AVG(Grade) from SC)

--(1).把低于总平均成绩的女同学成绩提高5%
Update SC
SET Grade = Grade * (1+0.05)
From SC, Student
Where Student.Sno = SC.Sno and Student.Sex = '女' and 
      SC.Grade < (Select AVG(Grade) from SC) 

Select * from SC

--(2).把SC复制为SC1
--先创建一个表,这里已经复制了，下面那个复制全部数据语句可以省略
Select * 
Into SC1 
From SC

--复制全部数据
Insert Into SC1
Select  *  From  SC1

--(3)从SC1中删除刘晨所有选课记录
DELETE 
FROM SC1
FROM Student
WHERE SC1.Sno = Student.Sno and Student.Sname = '刘晨'

Select * 
From SC1

--(4).检索每一门课程成绩都大于等于80分的学生学号、姓名和性别，并把检索到的值送往
--另一个已存在的基本表s1（Sno，SNAME，SEX）,如果s1不存在，自己创建
--先创建s1
Select * Into s1
FROM Student
--插入数据
INSERT INTO s1(Sno, SNAME, SEX)
Select distinct SC.Sno, Sname, Sex
From SC, Student
Where SC.Sno = Student.Sno and 
      SC.Sno NOT IN (Select Sno
                     From SC        
                      Where SC.Grade < 80)

Select * from SC

--(5)创建选课数少于3门的学生的视图SC_3(sno,sname)
Create View SC_3(sno, sname)
AS
Select SC.Sno, Sname
From SC, Student
Group by SC.Sno, Student.Sname, Student.Sno
Having Count(*) < 3 and SC.Sno = Student.Sno

--子查询  选课数少于3门的学生
Select SC.Sno, Count(*) as 选课数
From SC
Group by SC.Sno
Having Count(*) < 3

select * From SC_3

--作业二

select * from Student
select * from Course
select * from SC

--(1)取出没有选修‘操作系统’课程的学生姓名和年龄
Select distinct SC.Sno, Sname, Sage
From Student, Course, SC
Where Student.Sno = SC.Sno and Course.Cno = SC.Cno
and SC.Sno not in(
select distinct SC.Sno
From Course, SC
where Course.Cno = SC.Cno and Course.Cname = '操作系统')



 --(2)检索至少选修课程“数据结构”和“Ｃ语言”的学生学号。
 Select distinct SC.Sno
 From Course, SC
 where SC.Cno = Course.Cno and Course.Cname in ('数据结构', 'C语言')

 --(3)检索和“刘晨”同性别并同系的同学的姓名。
select Sname
from Student
Where Sex = 
            ( Select Sex
              From Student
              Where Sname = '刘晨')
     and Sdept = 
            ( Select Sdept
              From Student
              Where Sname = '刘晨')
                                    

--(4)求选修课程名为"数据结构"课程的学生的平均年龄；
Select AVG(Sage)
from Student, Course, SC
Where Student.Sno = SC.Sno and Course.Cno = SC.Cno and Course.Cname = '数据结构'


 --(5)查询没有选课的学生的学号和姓名
 Select Sno, Sname
 From Student
 Where Student.Sno not in 
                        ( select distinct SC.Sno
                          From Student, SC
                          where Student.Sno = SC.Sno )