MYSQL语句强化练习

之前发现自己写sql不怎么得心应手，总是百度零零散散的学习一下，所以在空闲的时候自己就专门找一下mysql的强化题敲一下练习一下，简要记录一下，sql写着写着就会越来越熟练，总之要自己加油！

表结构

学生表：Student(SNO,Sname,Sage,Sex)
课程表：Course(CNO,Cname,TNO)
成绩表：SC(SNO,CNO,score)
教师表：Teacher(TNO,Tname)

建表语句

create table student(
    id int primary key auto_increment comment '主键id',
    sno int not null comment '学号',
    sname varchar(100) comment '姓名',
    age int comment '年龄',
    sex int not null comment '性别0男1女'
)comment= '学生表'

create table course(
    id int primary key auto_increment comment '课程表主键id',
    cno int not null comment '课程号',
    cname varchar(100) comment '课程名',
    tno int not null comment '教师编号'
)comment = '课程表'

create table sc(
    id int primary key auto_increment comment '成绩表主键id',
    sno int not null comment '学号',
    cno int not null comment '课程号',
    score int not null comment '分数'
)comment = '成绩表'

create table teacher(
 id int primary key auto_increment comment '教师表主键id',
 tno int not null comment '教师编号',
 tname varchar(100) comment '教师姓名'
)comment = '教师表'

#1.查询“3001”课程比“3002”课程成绩高的所有学生的学号
select a.sno from
    (select sno,score from sc where cno=3001)a,
    (select sno,score from sc where cno=3002)b
where 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) 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
student.sno,
student.sname,
count(sc.cno),
sum(sc.score)
from student
left join sc on student.sno = sc.sno
group by student.sno

#4.查询姓“李”的教师数
select count(distinct(teacher.tname)) num
from teacher where teacher.tname like '李%'

#5.查询没有学过“李老师”课程的同学的学号、姓名
select
student.sno,
student.sname
from student
where student.sno not in
(
    select sc.sno from sc
    inner join course on sc.cno = course.cno
    inner join teacher on teacher.tno = course.tno
    where teacher.tname = '李老师'
)

#6.查询学过“王老师”所有课程的学生的学号、姓名
select student.sno,student.sname
from student where student.sno in
(
select sc.sno
from sc
inner join course on sc.cno = course.cno
inner join teacher on course.tno = teacher.tno
where teacher.tname = '王老师'
group by sc.sno
having count(sc.sno)=(
    select COUNT(course.cno) from teacher
    inner join course on teacher.tno = course.tno
    where teacher.tname = '王老师'
    )
)

#7.查询学过“3001”也学过“3004”课程的学生的学号、姓名
select student.sno,student.sname
from student
inner join sc on student.sno = sc.sno
where cno = 3001
and student.sno in (
    select sc.sno from sc where sc.cno=3004
)

select student.sno,student.sname
from student
inner join sc a on student.sno = a.sno
where cno = 3001
and EXISTS
(
    select b.sno from sc b where a.sno = b.sno and b.cno=3004
)

#8.查询所有课程成绩小于60的同学的学号、姓名
select stu.sno,stu.sname
from student stu
where stu.sno not in(
    select sc.sno from sc where sc.score >= 60 group by sc.sno
)

#9.查询没有学全所有课的同学的学号、姓名
select student.sno,student.sname
from student
inner join sc on student.sno = sc.sno
group by sc.sno having count(*)<
(
select count(cno) from course
)

#10.查询至少有一门课与学号为“1001”同学所学相同的学生的学号和姓名
select student.sno,student.sname
from student
inner join sc on student.sno = sc.sno
where sc.sno != 1001
and sc.cno in(
    select sc.cno from sc where sc.sno = 1001
)
group by student.sno

#11.查询和“1001”号的同学学习的课程完全相同的其他同学学号和姓名
select sc.sno
from sc where sc.sno != 1002 and cno in
(select cno from sc where sc.sno = 1002)
group by sno having count(*) =
(select count(*) from sc where sno = 1002)

#12.删除学习“李老师”课的sc表记录
delete sc
from sc
inner join course on course.cno = sc.cno
inner join teacher on teacher.tno = course.tno
where teacher.tname = '李老师'

#13.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“3004”课程的同学学号、3001号课程的平均成绩
insert into sc(sno,cno,score)
select sno,3001,(SELECT AVG(score) from sc where cno = 3001)
from student where sno not in
(
    select sno from sc where cno = 3003
)

#14.按平均成绩从高到低显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示：学生id，语文，数学，英语，有效课程数，有效平均分
select
s.sno as '学生id',
(select s1.score from sc s1 where s1.sno = s.sno and s1.cno = 3001) as '语文',
(select s2.score from sc s2 where s2.sno = s.sno and s2.cno = 3002) as '数学',
(select s3.score from sc s3 where s3.sno = s.sno and s3.cno = 3003) as '英语',
count(cno) as '有效课程数',
AVG(score) as '有效平均分'
from sc s group by s.sno order by '有效平均分'

#15.查询各科成绩最高和最低的分：以如下的形式显示，课程id，最高分，最低分
select
s.cno as '课程id',
(select max(score) from sc s1 where s1.cno = s.cno) as '最高分',
(select min(score) from sc s2 where s2.cno = s.cno) as '最低分'
from sc s group by s.cno

#16.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
s.cno as '课程id',
course.cname as '课程名',
AVG(s.score) as avgScore,
(select count(*) from sc s1 where s.cno = s1.cno and s1.score>60)/count(sno)*100 as rate
from sc s
inner join course on course.cno = s.cno
group by s.cno
order by avgScore asc,rate desc

#17.查询“3001”课程成绩在第2名到3名的学生的各科成绩
select
student.sname,course.cname,sc.score
from course
inner join sc on course.cno = sc.cno
and course.cno = 3001
inner join student on student.sno = sc.sno
order by sc.score desc
limit 1,2

#18.查询出只选修两门课程的全部学生的学号和姓名
select student.sno,student.sname
from student
inner join sc on student.sno = sc.sno
group by student.sno having count(student.sno)=2