# ###创建表
# 1、创建表 # 创建班级表 create table class( cid int primary key auto_increment, caption varchar(32) not null ); # 创建学生表 create table student( sid int primary key auto_increment, gender char(1) not null, class_id int not null, sname varchar(32) not null, foreign key(class_id) references class(cid) on delete cascade on update cascade ); # 创建老师表 create table teacher( tid int primary key auto_increment, tname varchar(32) not null ); # 创建课程表 create table course( cid int primary key auto_increment, cname varchar(32) not null, teacher_id int not null, foreign key(teacher_id) references teacher(tid) on delete cascade on update cascade ); # 创建成绩表 create table score( sid int primary key auto_increment, student_id int not null, course_id int not null, num int not null, foreign key(student_id) references student(sid) on delete cascade on update cascade, foreign key(course_id) references course(cid) on delete cascade on update cascade ); # 2、插入记录 # 班级表插入记录 insert into class values ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年一班'); # 学生表插入记录 insert into student values ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四'); # 老师表插入记录 insert into teacher values ('1', '张磊'), ('2', '李平'), ('3', '刘海燕'), ('4', '朱云海'), ('5', '李春秋'); # 课程表插入记录 insert into course values ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2'); # 成绩表插入记录 insert into score values ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('3', '1', '3', '76'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
1、查询所有的课程的名称以及对应的任课老师姓名
# 内联写法
select
course.cname,teacher.tname
from
course inner join teacher on course.teacher_id = teacher.tid
# where 写法
select
course.cname,teacher.tname
from
course,teacher
where
course.teacher_id = teacher.tid
2、查询学生表中男女生各有多少人
select
gender,count(*)
from
student
group by
gender
3、查询物理成绩等于100的学生的姓名
# inner join
select
student.sid,student.sname
from
course inner join score on course.cid = score.course_id
inner join student on score.student_id = student.sid
where
course.cname = "物理" and score.num = 100
# where 写法
select
student.sid,student.sname
from
course,score,student
where
course.cid = score.course_id
and
score.student_id = student.sid
and
course.cname = "物理"
and
score.num = 100
4、查询平均成绩大于八十分的同学的姓名和平均成绩
select
student_id,avg(num)
from
score
group by
student_id
having
avg(num)>80
# 内联写法
select
student_id,avg(num),student.sname
from
score inner join student on student.sid = score.student_id
group by
student_id
having
avg(num)>80
# where 写法
select
student_id,avg(num),student.sname
from
score,student
where
student.sid = score.student_id
group by
student_id
having
avg(num)>80
5、查询所有学生的学号，姓名，选课数，总成绩
# 选课数
select
student_id,count(*)
from
score
group by
student_id
# 总成绩
select
student_id,sum(num)
from
score
group by
student_id
# inner join 联一张student学生表
select
student_id,student.sname,count(*),sum(num)
from
score inner join student on score.student_id = student.sid
group by
student_id
# where
select
student_id,student.sname,count(*),sum(num)
from
score,student
where
score.student_id = student.sid
group by
student_id
# 附加需求(展现所有学生)
select
student.sid,student.sname,count(score.course_id),sum(num)
from
score right join student on score.student_id = student.sid
group by
student.sid
6、 查询姓李老师的个数
select
count(*)
from
teacher
where
tname like "李%"
7、 查询没有报李平老师课的学生姓名
# distinct 自动去重 例如:distinct(id)
# 1.报了李萍老师的课程的学生是谁?
select
distinct(score.student_id)
from
teacher,course,score
where
teacher.tid = course.teacher_id
and
course.cid = score.course_id
and
teacher.tname = "李平"
# 2.除了这些id的,就是没有报李萍老师课程的
select * from student where sid not in (1号)
# 3.综合拼接:
select student.sid,student.sname
from
student where sid not in (select
distinct(score.student_id)
from
teacher,course,score
where
teacher.tid = course.teacher_id
and
course.cid = score.course_id
and
teacher.tname = "李平")
8、 查询物理课程的分数比生物课程的分数高的学生的学号
# 1.物理课程的学生分数
select
score.student_id as t1id , course.cid, score.num
from
course inner join score on course.cid = score.course_id
where
course.cname = "物理"
# 2.生物课程的学生分数
select
score.student_id as t2id , course.cid, score.num
from
course inner join score on course.cid = score.course_id
where
course.cname = "生物"
# 3.综合拼装
select
*
from
(select
score.student_id as t1id , course.cid, score.num
from
course inner join score on course.cid = score.course_id
where
course.cname = "物理") as t1 inner join
(select
score.student_id as t2id , course.cid, score.num
from
course inner join score on course.cid = score.course_id
where
course.cname = "生物") as t2 on t1.t1id = t2.t2id
where
t1.num > t2.num
9、 查询没有同时选修物理课程和体育课程的学生姓名
# 1.找体育和物理课程的id
select
course.cid
from
course
where
cname="体育" or cname = "物理"
# 2.找选了体育或者物理课程的学生id
select
student_id
from
score
where
score.course_id in (1号)
# 拼装数据 查一下所有的id号
select
student_id
from
score
where
score.course_id in (select
course.cid
from
course
where
cname="体育" or cname = "物理")
# 3.(同时)选了物理和体育课程的学生id
select
score.student_id
from
score
where
score.course_id in (select course.cid from course where cname="体育" or cname = "物理")
group by
score.student_id
having
count(*) = 2
# 4.除了同时选择的这些学生id,剩下的就是没有同时选择的学生id
select
student.sid
from
student
where
student.sid not in (3号)
# 综合拼装:
select
student.sid,student.sname
from
student
where
student.sid not in (select
score.student_id
from
score
where
score.course_id in (select course.cid from course where cname="体育" or cname = "物理")
group by
score.student_id
having
count(*) = 2)
10、查询挂科超过两门(包括两门)的学生姓名和班级
select
score.student_id,student.sname,class.caption
from
score inner join student on student.sid = score.student_id
inner join class on class.cid = student.class_id
where
score.num < 60
group by
score.student_id
having
count(*) >= 2
11、查询选修了所有课程的学生姓名
# 1.先计算一下所有课程的总数
select count(*) from course;
# 2.按照学生分组,总数量是1号sql得出来的数据,满足条件
select
score.student_id,student.sname
from
score inner join student on score.student_id = student.sid
group by
score.student_id
having
count(*) = 4
# 3.综合拼接
select
score.student_id,student.sname
from
score inner join student on score.student_id = student.sid
group by
score.student_id
having
count(*) = (select count(*) from course)
12、查询李平老师教的课程的所有成绩记录
# 内联写法
select
course.cid,course.cname,score.student_id,score.num
from
teacher,course,score
where
course.teacher_id = teacher.tid
and
score.course_id = course.cid
and
teacher.tname = "李平"
# 1.找李平老师所有课程id
select
course.cid
from
teacher,course
where
teacher.tid = course.teacher_id
and
teacher.tname = "李平"
# 2.找所有分数
select
*
from
score
where
course_id in (2,4)
# 3.综合拼接
select
count(*)
from
score
where
course_id in (select
course.cid
from
teacher,course
where
teacher.tid = course.teacher_id
and
teacher.tname = "李平")
order by sid desc
13、查询全部学生都选修了的课程号和课程名
# 1.通过score表,找有成绩的学生个数
select
count(distinct student_id)
from
score
# 2.按照课程的种类分组,筛选出学生总数等于13(一个学科被13个人学习)
select
course_id
from
score
group by
course_id
having
count(*) = 13
# 综合拼装
select
course_id,course.cname
from
score,course
where
score.course_id = course.cid
group by
course_id
having
count(*) = (select
count(distinct student_id)
from
score)
14、查询每门课程被选修的次数
select
course_id,count(*)
from
score
group by
course_id
15、查询只选修了一门课程的学生学号和姓名
# 1.按照学生分进分类,统计总课数是1的;选一门
select
student_id
from
score
group by
student_id
having
count(*) = 1
# 2.顺带连一张学生表
select
student_id,student.sname
from
score,student
where
score.student_id = student.sid
group by
student_id
having
count(*) = 1
16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
select distinct(num) from score order by num desc
select distinct(num),student_id from score order by num desc
17、查询平均成绩大于85的学生姓名和平均成绩
# 1.先搜出来学生的id
select
score.student_id,avg(num)
from
score
group by
score.student_id
having
avg(num) > 85
# 2.顺带着联一张学生表student,找姓名
select
score.student_id,avg(num),student.sname
from
score inner join student on score.student_id = student.sid
group by
score.student_id
having
avg(num) > 85
18、查询生物成绩不及格的学生姓名和对应生物分数
select
student.sname,score.num,course.cname
from
course inner join score on score.course_id = course.cid
inner join student on score.student_id = student.sid
where
course.cname = "生物"
and
score.num<60
19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
# 1.找李平老师的课程id
select
course.cid
from
teacher,course
where
teacher.tid = course.teacher_id
and
teacher.tname = "李平"
# 2.按照学生分组,在选择里李平老师课程的情况下,找平均成绩最高的id
select
score.student_id
from
score
where
course_id in (2,4)
group by
score.student_id
order by
avg(num) desc limit 1
# 3.通过id 找出学生的姓名
select
score.student_id,student.sname
from
score,student
where
score.student_id = student.sid
and
course_id in (2,4)
group by
score.student_id
order by
avg(num) desc limit 1
20、查询每门课程成绩最好的课程id、学生姓名和分数
# 1.找分数的最大值,按照课程分类
select
course_id,max(num) as max_num
from
score
group by
score.course_id
# 2.找出该分数的所有数据
select
*
from
score t1
inner join (1号) t2 on t1.course_id = t2.course_id
inner join student t3 on t1.student_id = t3.sid
# 3.找需求中的对应字段
select
t2.max_num,t3.sname,t1.course_id
from
score t1
inner join (select
course_id,max(num) as max_num
from
score
group by
score.course_id) t2 on t1.course_id = t2.course_id
inner join student t3 on t1.student_id = t3.sid
where
t2.max_num = t1.num
21、查询不同课程但成绩相同的课程号、学生号、成绩
select
s1.student_id as s1_sid,
s2.student_id as s2_sid,
s1.course_id as s1_cid,
s2.course_id as s2_cid,
s1.num as s1_num,
s2.num as s2_num
from
score as s1,
score as s2
where
s1.num = s2.num
and
s1.course_id > s2.course_id
22、查询没学过“李平”老师课程的学生姓名以及选修的课程名称
# 1.找李平老师所有课程id
select
course.cid
from
teacher,course
where
teacher.tname = "李平"
and
teacher.tid = course.teacher_id
# 2.找学过李平老师课程的学生id
select
distinct(score.student_id)
from
score
where
course_id in (1号)
# 3.取反,除了这些学生的id,剩下的都没学过李平老师课程
# 方法一
select
student.sid ,student.sname,course.cname
from
student inner join score on student.sid = score.student_id
inner join course on course.cid = score.course_id
where
student.sid not in (2号)
# 方法二
select
student.sid ,student.sname,course.cname
from
student left join score on student.sid = score.student_id
left join course on course.cid = score.course_id
where
student.sid not in (2号)
23、查询所有选修了学号为2的同学选修过的一门或者多门课程的同学学号和姓名
# 1.找学号为2的学生,选了什么学科
select course_id from score where student_id = 2
# 2.找也选了1,3,4这些课程的学生id
select student_id from score where course_id in (1号)
# 需要去重,把必须的字段查询出来
select
distinct student_id,student.sname
from
score inner join student on student.sid = score.student_id
where
score.course_id in (1,3,4)
# 综合拼接
select
distinct student_id,student.sname
from
score inner join student on student.sid = score.student_id
where
score.course_id in (select course_id from score where student_id = 2)
24、任课最多的老师中学生单科成绩最高的课程id、学生姓名和分数
# 1.找出任课最多的老师,任课 "2" 门
select count(*) from course group by teacher_id order by count(*) desc limit 1
"""或者这样写"""
select count(cid) from course group by teacher_id order by count(cid) desc limit 1
# 2.找所有课程总数是2的老师id
select
teacher_id
from
course
group by
teacher_id
having
count(*) = (1号)
# 3.通过老师id,找到对应的课程
select cid from course where teacher_id = (2号)
# 4.通过该课程号找里面的最大分数
select
course_id,
max(num) as max_num
from
score
where
course_id in (3号)
group by
course_id
# 5.把最大分数,分数表,学生表拼在一起,做一次单表查询
select
t1.num,t2.max_num,t3.sid,t3.sname,t1.course_id
from
score t1 inner join (4号) t2 on t1.course_id = t2.course_id
inner join student t3 on t3.sid = t1.student_id
where
t1.num = t2.max_num
# 综合拼接:
select
t1.num,t2.max_num,t3.sid,t3.sname,t1.course_id
from
score t1 inner join (select
course_id,
max(num) as max_num
from
score
where
course_id in (select cid from course where teacher_id = (select
teacher_id
from
course
group by
teacher_id
having
count(*) = (select count(*) from course group by teacher_id order by count(*) desc limit 1)))
group by
course_id) t2 on t1.course_id = t2.course_id
inner join student t3 on t3.sid = t1.student_id
where
t1.num = t2.max_num