use StudentDB ;/**********************实验四 数据查询实验******************************/-- 1． 查询学生的基本信息；select *from Student;-- 2． 查询“CS”系学生的基本信息；select *from Student where Sdept='CS';-- 3． 查询“CS”系学生年龄不在19到21之间的学生的学号、姓名；select Sno,Sname from Studentwhere Sdept='CS' and Sage not between 19 and 21 ;-- 4． 找出最大年龄；select max(Sage) 最大年龄 from Student ;-- 5． 找出“CS”系年龄最大的学生，显示其学号、姓名；select Sno,Sname from Studentwhere Sdept='CS' and Sage= ( select max(Sage) from Student where sdept='CS');-- 6． 找出各系年龄最大的学生，显示其学号、姓名；************-- 本题用到了相关子查询，比较的难，需要多加练习update student set sage=23 where sno='200215125' ;select *from student;select sno,sname,sdeptfrom student awhere sage = ( select max(sage) from student b where a.sdept=b.sdept );-- 7． 统计“CS”系学生的人数；select count(*) 计算机系人数 from Studentwhere Sdept='CS';-- 8． 统计各系学生的人数，结果按升序排列；select Sdept,count(*) cntfrom SC,Studentwhere Student.Sno=SC.Sno group by Sdeptorder by cnt;-- 9． 按系统计各系学生的平均年龄，结果按降序排列；select Sdept,avg(Sage) agefrom SC,Studentwhere Student.Sno=SC.Snogroup by Sdeptorder by age desc;-- 10． 查询每门课程的课程名；select Cname from Course;-- 11． 查询无先修课的课程的课程名和学分数；select Cname,Ccreditfrom Coursewhere Cpno is null;-- 12． 统计无先修课的课程的学分总数；select sum(Ccredit) from Coursewhere Cpno is null ;-- 13． 统计每位学生选修课程的门数、学分及其平均成绩；select SC.sno,count(SC.Cno),sum(Ccredit),avg(Grade)from SC,Coursewhere SC.cno=Course.cnogroup by Sno;-- 14． 统计选修每门课程的学生人数及各门课程的平均成绩；select Cno,count(Cno),avg(Grade)from SCgroup by Cno;-- 15． 找出平均成绩在85分以上的学生，结果按系分组，并按平均成绩的升序排列；select Student.Sno,avg(grade) avg_grade,Sdeptfrom SC,Studentwhere SC.Sno=Student.Snogroup by Student.Sno,Sdepthaving avg(grade)>85order by avg_grade;select Student.Sno,avg(grade) avg_grade,Sdeptfrom SC join Studentusing(sno)group by Student.Sno,Sdepthaving avg_grade>85order by avg(grade) ; -- 注意在order by 后面可以用聚集函数-- 16． 查询选修了“1”或“2”号课程的学生学号和姓名；*********-- 方法一select distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and (Cno='1' or Cno='2' );-- 方法二select distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno in('1','2');-- 方法三select distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno='1'unionselect distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno='2' ;-- 17． 查询选修了“1”和“2”号课程的学生学号和姓名；*********select distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno='1' and Student.Sno in (select distinct Sno from SC where Cno='2' );/*-- intersect 在MySQL中没有select distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno='1'intersectselect distinct Student.Sno,Snamefrom Student,SCwhere SC.Sno=Student.Sno and Cno='2' ;*/-- 18． 查询选修了课程名为“数据库”且成绩在60分以下的学生的学号、姓名和成绩；insert into SC values('200215125','1',58);select Student.Sno,Sname,Gradefrom SC,Course,Studentwhere SC.Sno=Student.Sno and SC.Cno=Course.Cno and Cname='数据库' and grade<60 ;delete from SC where Sno='200215125' and Cno='1' ;-- 19． 查询每位学生选修了课程的学生信息（显示：学号，姓名，课程号，课程名，成绩）；select Student.Sno,Sname,Course.Cno,Cname,gradefrom Student,Course,SCwhere Student.Sno=SC.Sno and Course.Cno=SC.Cno;select sno,sname,cno,cname,gradefrom student join sc using(sno)join course using(cno);-- 20． 查询没有选修课程的学生的基本信息；*************-- 方法一select Student.* from Studentwhere Sno not in ( select Sno from SC );-- 方法二select Student.* from studentwhere not exists ( select * from SC where sno=Student.sno );-- 21． 查询选修了3门以上课程的学生学号；select Sno from SCgroup by Snohaving count(Sno)> 2;-- 22． 查询选修课程成绩至少有一门在85分以上的学生学号；select Sno from SCgroup by Snohaving max(Grade)>85 ;-- 23． 查询选修课程成绩均在85分以上的学生学号；select Sno from SCgroup by Snohaving min(Grade)>85 ;-- 24． 查询选修课程平均成绩在85分以上的学生学号；select Sno from SCgroup by Snohaving avg(Grade)>85 ;
