drop table if exists student;
create table student(
	sno varchar(10) primary key,
	sname varchar(20),
	sage int(2),
	sgender varchar(5)
);

drop table if exists teacher;
create table teacher(
	tno varchar(10) primary key,
	tname varchar(20)
);

drop table if exists course;
create table course(
	cno varchar(10),
	cname varchar(20),
	tno varchar(20),
	constraint pk_course primary key (cno,tno)
);

drop table if exists score;
create table score(
	sno varchar(10),
	cno varchar(10),
	score int(4),
	constraint pk_sc primary key (sno,cno)
);
=drop table if exists student;
create table student(
	-- 学号
	sno varchar(10) primary key,
	-- 姓名
	sname varchar(20),
	-- 年龄
	sage int(2),
	-- 性别
	sgender varchar(5)
);

drop table if exists teacher;
create table teacher(
	-- 老师编号
	tno varchar(10) primary key,
	-- 老师名字
	tname varchar(20)
);

drop table if exists course;
create table course(
	-- 课程编号
	cno varchar(10),
	-- 课程名字
	cname varchar(20),
	-- 老师标号
	tno varchar(20),
	constraint pk_course primary key (cno,tno)
);

drop table if exists score;
create table score(
	-- 
	sno varchar(10),
	cno varchar(10),
	score int(4),
	constraint pk_sc primary key (sno,cno)
);

/*******初始化学生表的数据******/  
insert into student values ('s001','张三',23,'男');  
insert into student values ('s002','李四',23,'男');  
insert into student values ('s003','吴鹏',25,'男');  
insert into student values ('s004','琴沁',20,'女');  
insert into student values ('s005','王丽',20,'女');  
insert into student values ('s006','李波',21,'男');  
insert into student values ('s007','刘玉',21,'男');  
insert into student values ('s008','萧蓉',21,'女');  
insert into student values ('s009','陈萧晓',23,'女');  
insert into student values ('s010','陈美',22,'女');  
commit;  
/******************初始化教师表***********************/  
insert into teacher values ('t001', '刘阳');  
insert into teacher values ('t002', '谌燕');  
insert into teacher values ('t003', '胡明星');  
commit;  
/***************初始化课程表****************************/  
insert into course values ('c001','J2SE','t002');  
insert into course values ('c002','Java Web','t002');  
insert into course values ('c003','SSH','t001');  
insert into course values ('c004','Oracle','t001');  
insert into course values ('c005','SQL SERVER 2005','t003');  
insert into course values ('c006','C#','t003');  
insert into course values ('c007','JavaScript','t002');  
insert into course values ('c008','DIV+CSS','t001');  
insert into course values ('c009','PHP','t003');  
insert into course values ('c010','EJB3.0','t002');  
commit;  
/***************初始化成绩表***********************/  
insert into sc values ('s001','c001',78.9);  
insert into sc values ('s002','c001',80.9);  
insert into sc values ('s003','c001',81.9);  
insert into sc values ('s004','c001',60.9);  
insert into sc values ('s001','c002',82.9);  
insert into sc values ('s002','c002',72.9);  
insert into sc values ('s003','c002',81.9);  
insert into sc values ('s001','c003','59');  
commit;

-- 1、查询"c001"课程比"c002"课程成绩高的所有学生的学号；
select a.sno
from 
(select * from sc a where a.cno = 'c001') a,
(select * from sc b where b.cno = 'c002') b
where a.sno = b.sno and a.score > b.score;

-- 或者

select a.sno 
from score a
where a.cno = 'c001' and exists(
    select b.sno 
    from score b
    where b.cno = 'c002' and a.score > b.score and a.sno = b.sno
)

-- 2、查询平均成绩大于60 分的同学的学号和平均成绩；
select sno,avg(score)
from sc 
group by sno
having avg(score) > 60
-- 3、查询所有同学的学号、姓名、选课数、总成绩；
select a.*,s.sname
from (
    select sno,sum(score),count(cno) 
    from sc group by sno
) a,student s
where a.sno = s.sno

-- 4、查询姓"刘"的老师的个数；
select count(tno)
from teacher
where tname like '刘%'
-- 5、查询没学过"谌燕"老师课的同学的学号、姓名；
select a.sno,a.sname
from student a
where a.sno not in(
    select distinct s.sno 
    from sc s,(
        select c.* 
        from course c,(
            select tno from teacher where tname = '谌燕'
        ) t
        where t.tno = c.tno
    ) b
    where s.cno = b.cno
)
-- 或者
select a.sno,a.sname
from student a
where a.sno not in(
    select distinct sno 
    from sc s
    join course c on s.cno = c.cno
    join teacher t on c.tno = t.tno 
    where tname = '谌燕'
)
-- 6、查询学过"c001"并且也学过编号"c002"课程的同学的学号、姓名；
select stu.*
from student stu
join sc a
on stu.sno = a.sno
join sc b
on stu.sno = b.sno
-- 7、查询学过"谌燕"老师所教的所有课的同学的学号、姓名；
select stu.sno,stu.sname
from student stu
join sc 
on sc.sno = stu.sno
join course
on course.cno = sc.cno
join teacher t
on t.tno = course.tno
where t.tname = '谌燕'
-- 8、查询课程编号"c002"的成绩比课程编号"c001"课程低的所有同学的学号、姓名；
select stu.sno,stu.sname
from student stu
join sc a
on stu.sno = a.sno
join sc b
on stu.sno = b.sno
where a.cno = 'c001' and b.cno = 'c002' and a.score < b.score
-- 9、查询所有课程成绩小于60 分的同学的学号、姓名；
select stu.sno,stu.sname
from student stu
join sc 
on sc.sno = stu.sno
where sc.score < 60
-- 10、查询没有学全所有课的同学的学号、姓名；
select stu.sno,stu.sname,count(sc.cno)
from student stu
left join sc 
on stu.sno = sc.sno
group by stu.sno,stu.sname
having count(sc.cno) < (
    select count(distinct cno) from course
)

-- 11、查询至少有一门课与学号为"s001"的同学所学相同的同学的学号和姓名；
select st.*
from student st,
(select distinct a.sno from 
 (select * from sc) a,
 (select * from sc where sc.sno = 's001') b
 where a.cno = b.cno
) h
where st.sno = h.sno and st.sno<>'s001'
-- 12、查询至少学过学号为"s001"同学所有一门课的其他同学学号和姓名；
select * from sc
 left join student st on st.sno=sc.sno
 where sc.sno<>'s001' 
 and sc.cno in (select cno from sc where sno='s001')
-- 13、把"SC"表中"谌燕"老师教的课的成绩都更改为此课程的平均成绩；
update sc c set score=
 (
     select avg(c.score)  from course a,teacher b 
     where a.tno=b.tno and b.tname='谌燕' and a.cno=c.cno 
     group by c.cno
 )
where cno in( select cno from course a,teacher b where a.tno=b.tno and b.tname='谌燕')
-- 14、查询和"s001"号的同学学习的课程完全相同的其他同学学号和姓名；
-- select* from sc where sno<>'s001'
-- minus
-- ( select* from sc minus select * from sc where sno='s001')
--  TODO

-- 15、删除学习"谌燕"老师课的SC 表记录；
delete from sc where sc.cno in
(
    select cno from course c
    left join teacher t on  c.tno=t.tno
    where t.tname='谌燕'
)
-- 16、向SC 表中插入一些记录，这些记录要求符合以下条件：没有上过编号"c002"课程的同学学号、"c002"号课的平均成绩；
insert into sc (sno,cno,score)
 select distinct st.sno,sc.cno,(select avg(score)from sc where cno='c002')
 from student st,sc
 where not exists
 (select * from sc where cno='c002' and sc.sno=st.sno) and sc.cno='c002';
-- 17、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
select cno ,max(score),min(score) from sc group by cno;
-- 18、按各科平均成绩从低到高和及格率的百分数从高到低顺序
select cno,avg(score),sum(case when score>=60 then 1 else 0 end)/count(*) as 及格率
from sc group by cno
order by avg(score) , 及格率 desc
-- 19、查询不同老师所教不同课程平均分从高到低显示
select max(t.tno),max(t.tname),max(c.cno),max(c.cname),c.cno,avg(score) from sc , course c,teacher t
where sc.cno=c.cno and c.tno=t.tno
group by c.cno
order by avg(score) desc
-- 20、统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]
select sc.cno,c.cname,
sum(case  when score between 85 and 100 then 1 else 0 end) AS "[100-85]",
sum(case  when score between 70 and 85 then 1 else 0 end) AS "[85-70]",
sum(case  when score between 60 and 70 then 1 else 0 end) AS "[70-60]",
sum(case  when score <60 then 1 else 0 end) AS "[<60]"
from sc, course c
where  sc.cno=c.cno
group by sc.cno ,c.cname;
-- 21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
-- select * from
-- (select sno,cno,score,row_number()over(partition by cno order by score desc) rn from sc)
-- where rn<4
-- TODO

-- 22、查询每门课程被选修的学生数
select cno,count(sno)from sc group by cno;
-- 23、查询出只选修了一门课程的全部学生的学号和姓名
select sc.sno,st.sname,count(cno) from student st
left join sc
on sc.sno=st.sno
group by st.sname,sc.sno having count(cno)=1;
-- 24、查询男生、女生人数
select sgender,count(*)from student group by sgender;
-- 25、查询姓"张"的学生名单
select * from student where sname like '张%';
-- 26、查询同名同性学生名单，并统计同名人数
select sname,count(*)from student group by sname having count(*)>1;
-- 27、1995 年出生的学生名单(注：Student 表中Sage 列的类型是int)
select sno,sname,sage,sgender from student t where YEAR(NOW())-sage = 1995
-- 28、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列 
select cno,avg(score) from sc group by cno order by avg(score)asc,cno desc;
-- 29、查询平均成绩大于85 的所有学生的学号、姓名和平均成绩
select st.sno,st.sname,avg(score) from student st
left join sc on sc.sno=st.sno
group by st.sno,st.sname having avg(score)>85;
-- 30、查询课程名称为"数据库"，且分数低于60 的学生姓名和分数
select sname,score from student st,sc,course c
where st.sno=sc.sno and sc.cno=c.cno and c.cname='Oracle' and sc.score<60
-- 31、查询所有学生的选课情况； 
select st.sno,st.sname,c.cname from student st,sc,course c
where sc.sno=st.sno and sc.cno=c.cno;
-- 32、查询任何一门课程成绩在70 分以上的姓名、课程名称和分数；
select st.sname,c.cname,sc.score from student st,sc,course c
where sc.sno=st.sno and sc.cno=c.cno and sc.score>70
-- 33、查询不及格的课程，并按课程号从大到小排列
select sc.sno,c.cname,sc.score from sc,course c
where sc.cno=c.cno and sc.score<60 order by sc.cno desc;
-- 34、查询课程编号为c001 且课程成绩在80 分以上的学生的学号和姓名；
select st.sno,st.sname,sc.score from sc,student st
where sc.sno=st.sno and cno='c001' and score>80;
-- 35、求选了课程的学生人数
select count(distinct sno) from sc;
-- 36、查询选修"谌燕"老师所授课程的学生中，成绩最高的学生姓名及其成绩
select st.sname,score from student st,sc ,course c,teacher t
where
st.sno=sc.sno and sc.cno=c.cno and c.tno=t.tno and t.tname='谌燕' and sc.score=
(select max(score)from sc where sc.cno=c.cno)
-- 37、查询各个课程及相应的选修人数
select cno,count(sno) from sc group by cno;
-- 38、查询不同课程成绩相同的学生的学号、课程号、学生成绩
select a.* from sc a ,sc b where a.score=b.score and a.cno<>b.cno
-- 39、查询每门功课成绩最好的前两名
-- select * from (
--  select sno,cno,score,row_number()over(partition by cno order by score desc) my_rn from sc t
-- )
-- where my_rn<=2
-- TODO

-- 40、统计每门课程的学生选修人数（超10 人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，
--  若人数相同，按课程号升序排列
select cno,count(sno) from sc 
group by cno having count(sno)>10
order by count(sno) desc,cno asc;
-- 41、检索至少选修两门课程的学生学号
select sno from sc group by sno having count(cno)>1;

-- 42、查询全部学生都选修的课程的课程号和课程名
select distinct(c.cno),c.cname from course c ,sc where sc.cno=c.cno
或
select cno,cname from course c where c.cno in (select cno from sc group by cno)
-- 43、查询没学过"谌燕"老师讲授的任一门课程的学生姓名
select st.sname from student st
where st.sno not in
(select distinct sc.sno from sc,course c,teacher t where sc.cno=c.cno and c.tno=t.tno and t.tname='谌燕')
-- 44、查询两门以上不及格课程的同学的学号及其平均成绩
select sno,avg(score)from sc
where sno in
(
    select sno from sc where sc.score<60
    group by sno having count(sno)>1
) group by sno
-- 45、检索"c004"课程分数小于60，按分数降序排列的同学学号

select sno from sc where cno='c004' and score<90 order by score desc;
-- 46、删除"s002"同学的"c001"课程的成绩
delete from sc where sno='s002' and cno='c001';