轻量级的建模工具： https://erdplus.com/
导入数据
学生表
create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10)); insert into Student values('01' , '赵雷' , '1990-01-01' , '男'); insert into Student values('02' , '钱电' , '1990-12-21' , '男'); insert into Student values('03' , '孙风' , '1990-05-20' , '男'); insert into Student values('04' , '李云' , '1990-08-06' , '男'); insert into Student values('05' , '周梅' , '1991-12-01' , '女'); insert into Student values('06' , '吴兰' , '1992-03-01' , '女'); insert into Student values('07' , '郑竹' , '1989-07-01' , '女'); insert into Student values('09' , '张三' , '2017-12-20' , '女'); insert into Student values('10' , '李四' , '2017-12-25' , '女'); insert into Student values('11' , '李四' , '2017-12-30' , '女'); insert into Student values('12' , '赵六' , '2017-01-01' , '女'); insert into Student values('13' , '孙七' , '2018-01-01' , '女');
科目表
create table Course(CId varchar(10),Cname nvarchar(10),TId varchar(10)); insert into Course values('01' , '语文' , '02'); insert into Course values('02' , '数学' , '01'); insert into Course values('03' , '英语' , '03');
教师表
create table Teacher(TId varchar(10),Tname varchar(10)); insert into Teacher values('01' , '张三'); insert into Teacher values('02' , '李四'); insert into Teacher values('03' , '王五');
成绩表
create table SC(SId varchar(10),CId 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);
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 * from sc a left join student d on a.sid=d.sid inner join sc b on a.sid=b.sid and a.cid='01' and b.cid='02'
where a.score>b.score;
1.1 查询同时存在" 01 "课程和" 02 "课程的情况
select * from sc a inner join sc b on a.sid=b.sid and a.cid='01' and b.cid='02';
select * from (select * from sc a left join sc b on a.sid=b.sid and a.cid='01' and b.cid='02'where b.score is not null) a;
-- 1.2 查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )
select * from sc a left join sc b on a.sid=b.sid and a.cid='01' and b.cid='02' where a.Cid=01;
-- 1.3 查询不存在" 01 "课程但存在" 02 "课程的情况
-- 先把01课程的筛选出来
select* from sc where sid not in(select sid from sc where cid='01') and cid='02';
2.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.sid,
sname,
avg(score)
from
sc a inner join student b
on a.sid=b.sid
GROUP BY a.sid
having avg(score)>60;
-- 3.查询在 SC 表存在成绩的学生信息
select
b.*
from sc a left join student b on
a.sid=b.sid
group by sid;
-- 4.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
a.sid,
a.sname,
count(a.sid),
sum(b.score)
from student a
left join sc b
on a.sid=b.sid
group by a.sid;
-- 4.1 查有成绩的学生信息
select
b.*
from sc a
left join student b
on a.sid=b.sid
group by a.sid;
-- 5.查询「李」姓老师的数量
select
*
from teacher
where tname like '李%';
-- 6.查询学过「张三」老师授课的同学的信息
select student.*
from student
where sid in (select sid
from sc
where cid=(select a.cid
from course a inner join teacher b
on a.tid=b.tid where b.tname='张三'));
-- 7.查询没有学全所有课程的同学的信息
select a.*,
count(cid) as c_count
from student a inner join sc b
on a.sid = b.sid
group by a.sid
having c_count<(select count(cid) from course);
-- 8.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 distinct b.* from sc a left join student b on a.sid=b.sid where cid in (select cid from sc where sid='01');
-- 9.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
select c.*
from student c inner join
(select sid,group_concat(cid order by cid asc) as courses
from sc group by sid) a
inner join (select sid,group_concat(cid order by cid asc) as courses from sc group by sid having sid = 01) b
on a.sid != 01 and a.courses = b.courses and c.sid = a.sid;
-- 11.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
b.sid,
b.sname,
avg(score)
from sc a
left join student b
on a.sid=b.sid
inner join (select
sid
from sc
where score<60
GROUP BY sid
HAVING count(sid)>=2) c
on a.sid=c.sid
group by a.sid;
-- 13.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
sid,
sum(score),
avg(score)
from sc
GROUP BY sid
order by avg(score) desc;
