数据库练习

参考网站：https://blog.csdn.net/flycat296/article/details/63681089#commentBox

练习的数据表结构

–1.学生表
Student(S,Sname,Sage,Ssex)
–S 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

–2.课程表
Course(C,Cname,T#)
–C --课程编号,Cname 课程名称,T# 教师编号

–3.教师表
Teacher(T,Tname)
–T 教师编号,Tname 教师姓名

–4.成绩表
SC(S,C,score)
–S 学生编号,C 课程编号,score 分数

数据表中的数据

create table Student(S varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10));
insert into Student values('01' , N'赵雷' , '1990-01-01' , N'男');
insert into Student values('02' , N'钱电' , '1990-12-21' , N'男');
insert into Student values('03' , N'孙风' , '1990-05-20' , N'男');
insert into Student values('04' , N'李云' , '1990-08-06' , N'男');
insert into Student values('05' , N'周梅' , '1991-12-01' , N'女');
insert into Student values('06' , N'吴兰' , '1992-03-01' , N'女');
insert into Student values('07' , N'郑竹' , '1989-07-01' , N'女');
insert into Student values('08' , N'王菊' , '1990-01-20' , N'女');


create table Course(C varchar(10),Cname nvarchar(10),T varchar(10));
insert into Course values('01' , N'语文' , '02');
insert into Course values('02' , N'数学' , '01');
insert into Course values('03' , N'英语' , '03');

#教师表 Teacher
create table Teacher(T varchar(10),Tname nvarchar(10));
insert into Teacher values('01' , N'张三');
insert into Teacher values('02' , N'李四');
insert into Teacher values('03' , N'王五');

#成绩表 SC
create table SC(S varchar(10),C varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

练习题以及sql语句

1.查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数

select A.*,B.C,B.score from (select * from SC where C='01')A 
left join(select * from SC where C='02')B on A.S=B.S 
where A.score>B.score

2.查询同时存在" 01 “课程和” 02 "课程的情况
（两个条件查询，可采用内连接）

select * from (select * from SC where C='01')A 
inner join(select * from SC where C='02')B on A.S=B.S 
#select * from SC where C='01' and C='02'

3、查询不存在" 01 “课程但存在” 02 "课程的情况

select s from sc where sc.c='02' and s not in (select s from sc where c='01')

5、查询所有人的平均成绩

select S,AVG(score)dc from SC group by S

6、查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

select A.s,B.Sname,A.dc from(select s,avg(score)dc from sc group by s)A 
inner join student B on A.s=B.s 

7、其它

#查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数
select A.*,B.C,B.score from (select * from SC where C='01')A 
left join(select * from SC where C='02')B on A.S=B.S 
where A.score>B.score;

#查询同时存在" 01 "课程和" 02 "课程的情况（两个条件查询，可采用内连接）
select * from (select * from SC where C='01')A 
inner join(select * from SC where C='02')B on A.S=B.S ;
#select * from SC where C='01' and C='02';

#查询不存在" 01 "课程但存在" 02 "课程的情况
select s from sc where sc.c='02' and s not in (select s from sc where c='01');

#查询所有人的平均成绩
select S,AVG(score)dc from SC group by S;

#查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
select A.s,B.Sname,A.dc from(select s,avg(score)dc from sc group by s)A 
inner join student B on A.s=B.s;

#查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩
select A.s,B.Sname,A.dc from(select s,avg(score)dc from sc group by s)A 
inner join student B on A.s=B.s ;

#查询在 SC 表存在成绩的学生信息(distinct的应用)
select B.S,B.Sname,B.Sage,B.Ssex from(select s from sc group by s)A 
inner join student B on A.s=B.s;
select * from Student where S in (select distinct S from SC);

#查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为null)
select B.s,B.Sname,A.y,A.x from (select s,sum(score)x,count(C)y from sc group by s)A
right join student B on A.s=B.s;

#查有成绩的学生信息
select * from student where s in (select distinct s from sc);

#查询「李」姓老师的数量 
select count(*) from teacher where Tname like '李%';

#查询学过「张三」老师授课的同学的信息
select * from student 
where s in (select s from sc 
where C=(select C from course 
where T=(select T from teacher where Tname like '李%')));

#查询没有学全所有课程的同学的信息
select * from student where s in (select s from sc group by s having count(c)>=3);

#查询至少有一门课与学号为" 01 "的同学所学相同的同学的信息
select * from student where s in (select s from sc where c in (select c from sc where s='01'));

#查询和" 01 "号的同学学习的课程完全相同的其他同学的信息

#查询没学过「张三」老师讲授的任一门课程的学生姓名
select * from student where s not in (select s from sc where c=(select C from course where c=(select T from teacher where Tname='张三')));

#查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
select A.s,A.sname,B.x from student A right join (select s,avg(score)x from sc where s in (select s from sc where score<60 group by s having count(c)>=2) group by s)B on A.s=B.s;

#检索" 01 "课程分数小于 60 ，按分数降序排列的学生信息
select s,score from sc where C='01' and score<60 order by score desc;

#按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
select S,case when C='01' then score else 0 end'01',
case C when '02' then score else 0 end'02',
case C when '03' then score else 0 end'03',AVG(score)平均分 from SC
group by S order by 平均分 desc;