【建表并导入数据】
--建表
--学生表
CREATE TABLE `Student`(
`s_id` VARCHAR(20),
`s_name` VARCHAR(20) NOT NULL DEFAULT '',
`s_birth` VARCHAR(20) NOT NULL DEFAULT '',
`s_sex` VARCHAR(10) NOT NULL DEFAULT '',
PRIMARY KEY(`s_id`)
);
--课程表
CREATE TABLE `Course`(
`c_id` VARCHAR(20),
`c_name` VARCHAR(20) NOT NULL DEFAULT '',
`t_id` VARCHAR(20) NOT NULL,
PRIMARY KEY(`c_id`)
);
--教师表
CREATE TABLE `Teacher`(
`t_id` VARCHAR(20),
`t_name` VARCHAR(20) NOT NULL DEFAULT '',
PRIMARY KEY(`t_id`)
);
--成绩表
CREATE TABLE `Score`(
`s_id` VARCHAR(20),
`c_id` VARCHAR(20),
`s_score` INT(3),
PRIMARY KEY(`s_id`,`c_id`)
);
--插入学生表测试数据
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('08' , '王菊' , '1990-01-20' , '女');
--课程表测试数据
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');
--教师表测试数据
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
--成绩表测试数据
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);
笔试题
*1、查询课程编号为“01”的课程比“02”的课程成绩高的所有学生的学号。
思路：使用自联结把01课程当作表a查出成绩，02课程当作表b查出成绩，表a和表b的学号相等，保证查询的是同一个人，然后进行成绩的比较
-- 写法一：
select a.s_id
from Score a join Score b on a.s_id = b.s_id and a.s_score >b.s_score
where a.c_id = '01' and b.c_id= '02';
-- 写法二：
select a.s_id
from (select * from Score where c_id = '01') as a
join (select * from Score where c_id='02') as b
on a.s_id = b.s_id
where a.s_score > b.s_score;
2、查询平均成绩大于60分的学生的学号和平均成绩
思路: 按学号进行分组，计算出每个学生各科的成绩，然后求出平均成绩
select s_id, avg(s_score)
from Score
group by s_id
having avg(s_score)>60;
3、查询所有学生的学号、姓名、选课数、总成绩
思路：姓名属于Student表，其它属于Score表，考虑内联结
select Score.s_id, Student.s_name,count(c_id),sum(s_score)
from Score join Student on Score.s_id = Student.s_id
group by s_id,s_name;
4、查询姓“张”的老师的个数
思路：like的用法
select count(t_id)
from Teacher
where t_name like '张%';
*5.查询没学过“张三”老师课的学生的学号、姓名(重点)
思路: 查出张三老师教过什么课，并把张三老师教过的课当作一张表，而查询的学生不在这张表中
select s_id, s_name
from Student
where s_id not in
(select s_id from Score join Course on Score.c_id = Course.c_id
join Teacher on Course.t_id = Teacher.t_id
where t_name = '张三');
6、查询学过“张三”老师所教的所有课的同学的学号、姓名
select s_id, s_name
from Student
where s_id in
(select s_id from Score join Course on Score.c_id = Course.c_id
join Teacher on Course.t_id = Teacher.t_id
where t_name = '张三');
*7、查询学过编号为“01”的课程并且也学过编号为“02”的课程的学生的学号、姓名
自联结。把学过表01课程的学生当作表a，学过02课程的学生当作表b，分别从这两张表中取出同一个学生学习过的课程
select s_id, s_name
from Student
where s_id in
(select a.s_id from
(select s_id from Score where c_id = '01') as a
join (select s_id from Score where c_id ='02') as b
on a.s_id= b.s_id);
8、查询课程编号为“02”的总成绩
select sum(s_score)
from Score
where c_id = '02';
9、查询所有课程成绩小于60分的学生的学号、姓名
思路：按学生进行分组，查询每个学生所有课程的成绩
select Student.s_id, Student.s_name
from Student join Score on Student.s_id= Score.s_id
where Score.s_score <60
group by s_id, s_name;
10、查询没有学全所有课的学生的学号、姓名
思路：按学生进行分组，查出每个学生学习课程的数量，再跟课程总数相比
select Student.s_id, Student.s_name
from Student join Score on Score.s_id = Student.s_id
group by s_id, s_name
having count(Score.c_id) < (select count(c_id) from Course);
*11、查询至少有一门课与学号为“01”的学生所学课程相同的学生的学号和姓名
思路：1. 查出01学生学了什么课程；2. 查询出的结果要排除01学生
select distinct Student.s_id, Student.s_name
from Student join Score on Student.s_id= Score.s_id
where c_id in
(select c_id from Score where s_id = '01')
and Student.s_id<>'01';
*12、查询和“01”号同学所学课程完全相同的其他同学的学号
思路：课程完全相同表示学习的科目相同，学习的课程数也相同。
select s_id
from Score
where c_id in
(select c_id from Score where s_id='01')
and s_id <> '01'
group by s_id
having count(c_id)=(select count(c_id) from Score where s_id='01');
*13、把“SCORE”表中“张三”老师教的课的成绩都更改为此课程的平均成绩
思路：表有主键的情况下，不可以使用insert，应该使用update。使用update需要注意：set不能接复杂条件。把Score当成一张表，把计算出张三老师教的课的平均成绩当作另外一张表
update Score as a
join
(select avg(s_score) as t, Score.c_id from Score join Course on Score.c_id= Course.c_id
join Teacher on Teacher.t_id= Course.t_id
where t_name ='张三'
group by c_id) as b
on a.c_id= b.c_id
set a.s_score= b.t;
14、查询和“02”号的同学学习的课程完全相同的其他同学学号和姓名(同12题）
15、删除学习“张三”老师课的SC表记录
delete from Score
where c_id in
(select c_id from Course join Teacher on Course.t_id=Teacher.t_id
where t_name ='张三');
*17、按平均成绩从高到低显示所有学生的“数据库”（c_id='04'）、“企业管理”（c_id='01'）、“英语”（c_id='06'）三门的课程成绩，按如下形式显示：学生ID，数据库，企业管理，英语，有效课程数，有效平均分
思路：按学生进行分组，显示学生各科成绩。由于科目唯一时，会返回多个值（例如查询数据库的成绩，会返回多个学生对应数据库的成绩），此时应注意使用别名进行区别嵌套
select s_id as '学生ID',
(select s_score from Score where Score.s_id= sc.s_id and c_id = '04') as '数据库',
(select s_score from Score where Score.s_id= sc.s_id and c_id = '01') as '企业管理',
(select s_score from Score where Score.s_id= sc.s_id and c_id = '06') as '英语',
count(c_id) as 有效课程数,
avg(s_score) as 有效平均分
from Score as sc
group by s_id
order by avg(s_score) DESC;
18、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
思路：按科目进行分组
select c_id as 课程ID,
max(s_score) as 最高分,
min(s_score) as 最低分
from Score
group by c_id;
*19、按各科平均成绩从低到高和及格率的百分数从高到低排列，以如下形式显示：课程号,课程名,平均成绩,及格百分数
思路：及格百分数=及格率=及格人数/总人数。
select Course.c_id as '课程号',
Course.c_name as '课程名',
avg(Score.s_score) as '平均成绩',
concat(d.c/a.b*100,'%') as '及格百分数'
from (select c_id,count(distinct s_id) as b from Score group by c_id) as a
join (select c_id,count(distinct s_id) as c from Score where s_score >=60 group by c_id) as d
on a.c_id=d.c_id
join Course on a.c_id=Course.c_id
join Score on Course.c_id=Score.c_id
group by Course.c_id,Course.c_name
order by 平均成绩, 及格百分数 DESC;
20、查询如下课程平均成绩和及格率的百分数（用1行显示），其中企业管理为001，马克思为002，UML为003，数据库为004
略
21、查询不同老师所教不同课程平均分从高到低显示
思路：按老师、科目进行分组，不同表之间要内联结
select Teacher.t_id,Teacher.t_name,Course.c_name,avg(Score.s_score)
from Teacher join Course on Teacher.t_id=Course.t_id
join Score on Course.c_id=Score.c_id
group by t_id,t_name,c_name
order by avg(Score.s_score) DESC;
*23、使用分段[100-85],[85-70],[70-60],[<60]来统计各科成绩，分别统计各分数段人数：课程ID和课程名称
思路：case表达式的用法
select Course.c_id, Course.c_name,
sum(case when Score.s_score between 85 and 100 then 1 else 0 end) as '优秀',
sum(case when Score.s_score between 70 and 85 then 1 else 0 end) as '良好',
sum(case when Score.s_score between 60 and 70 then 1 else 0 end) as '及格',
sum(case when Score.s_score<60 then 1 else 0 end) as '不及格'
from Score join Course on Score.c_id=Course.c_id
group by c_id,c_name;
*24、查询学生平均成绩及其名次
思路：名次排序使用rank按平均成绩降序排序
select s_id, avg(s_score), rank() over (order by avg(s_score) DESC)
from Score
group by s_id;
*25、查询各科成绩前三名的记录（不考虑成绩并列情况）
思路：从排序好名次的表中取数据，因不考虑并列，因此使用row_number进行排序
select c_id, s_score
from (select *, row_number () over (partition by c_id order by s_score DESC) as a from Score) as b
where a in(1,2,3);
26、查询每门课程被选修的学生数
select c_id, count(s_id)
from Score
group by c_id;
27、查询出只选修了两门课程的全部学生的学号和姓名
select Student.s_id,Student.s_name, count(Score.c_id)
from Student join Score on Student.s_id= Score.s_id
group by s_id,s_name
having count(c_id)=2;
28、查询男生、女生人数
思路：按性别进行分组，分别计算不同分组的性别数
select s_sex, count(s_sex)
from Student
group by s_sex;
29、查询名字中含有“风”字的学生信息
select *
from Student
where s_name like '%风%';
30、查询同名同姓学生名单并统计同名人数
思路：按学生姓名进行分组，然后查询每组人数，若同名同姓，则分组中人数会大于1
select s_name, count(s_id)
from Student
group by s_name
having count(s_id)>1;
31、1990年出生的学生名单（注：Student表中s_birth列的类型是datetime）
思路：可以用like取出相关年份，也可以用year
-- 方法一
select s_name
from Student
where s_birth like '1990%';
-- 方法二
select s_name
from Student
where year(s_birth)=1990;
32、查询平均成绩大于85的所有学生的学号、姓名和平均成绩
思路：按学生进行分组
select Student.s_id, Student.s_name, avg(Score.s_score)
from Student join Score on Student.s_id=Score.s_id
group by s_id,s_name
having avg(Score.s_score) >85;
33、查询每门课程的平均成绩，结果按平均成绩升序排序，平均成绩相同时，按课程号降序排列
select c_id, avg(s_score)
from Score
group by c_id
order by avg(s_score),c_id DESC;
34、查询课程名称为“数学”且分数低于60的学生姓名和分数
select Student.s_name, Score.s_score
from Student join Score on Student.s_id=Score.s_id
join Course on Course.c_id=Score.c_id
where Course.c_name='数学'
and Score.s_score <60;
35、查询所有学生的选课情况
select Student.s_id, Student.s_name, Course.c_id, Course.c_name
from Student join Score on Student.s_id=Score.s_id
join Course on Score.c_id=Course.c_id
group by Student.s_id, Student.s_name, Course.c_id, Course.c_name;
36、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 Student.s_name,Course.c_name,Score.s_score
from Student join Score on Student.s_id=Score.s_id
join Course on Score.c_id=Course.c_id
where s_score >70
group by Student.s_name,Course.c_name,Score.s_score;
37、查询不及格的课程并按课程号从大到小排列
select Score.c_id, Course.c_name,Score.s_id,Student.s_name
from Score join Course on Score.c_id=Course.c_id
join Student on Student.s_id=Score.s_id
where Score.s_score<60
order by c_id DESC;
38、查询课程编号为03且课程成绩在80分以上的学生的学号和姓名
select Student.s_id,Student.s_name
from Student join Score on Student.s_id=Score.s_id
where Score.c_id='03'
and Score.s_score>80;
39、查询选了课程的学生人数
select c_id,count(s_id)
from Score
group by c_id;
*40、查询选修“张三”老师所授课程的学生中成绩最高的学生姓名及其成绩
思路：查出张三老师教了哪些学生，然后把这些学生的成绩进行排序，选择第一名
select Student.s_name, Score.s_score
from Student join Score on Student.s_id=Score.s_id
where Score.s_id in
(select Score.s_id from Score join Course on Score.c_id=Course.c_id
join Teacher on Course.t_id=Teacher.t_id
where t_name='张三')
order by Score.s_score DESC
limit 1;
41、查询各个课程及相应的选修人数
select c_id, count(s_id)
from Score
group by c_id;
*42、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
思路：不同课程说明c_id不同
select distinct a.s_id,a.c_id,a.s_score
from Score a join Score b
on a.s_id=b.s_id and a.c_id<> b.c_id
where a.s_score=b.s_score;
43、查询每门课程成绩最好的前两名
select s_id, c_id, s_score
from (select *,rank() over (partition by c_id order by s_score DESC) as b from Score) as a
where b in (1,2);
44、统计每门课程的学生选修人数(超过5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序，若人数相同，按课程号升序排序
select c_id, count(s_id)
from Score
group by c_id
having count(s_id)>5
order by count(s_id) DESC,c_id;
45、查询至少选修两门课程的学生学号
select s_id
from Score
group by s_id
having count(c_id)>=2;
46、查询选修了全部课程的学生信息
思路：该学生的选修课数量等于可供选择的所有选修课数量之和
select Student.s_id, Student.s_name,Student.s_birth, Student.s_sex
from Student join Score on Student.s_id=Score.s_id
group by Student.s_id, Student.s_name,Student.s_birth, Student.s_sex
having count(Score.c_id)=(select count(distinct c_id) from Score);
47、查询没学过“张三”老师讲授的任一门课程的学生姓名
select s_name
from Student
where s_id not in
(select Score.s_id from Score join Course on Score.c_id=Course.c_id
join Teacher on Teacher.t_id=Course.t_id
where t_name = '张三');
48、查询两门以上不及格课程的同学的学号及其平均成绩
select s_id, avg(s_score)
from Score
where s_score <60
group by s_id
having count(c_id)>=2;
49、检索课程编号为“04”且分数小于60的学生学号，结果按按分数降序排列
select s_id
from Score
where c_id='04'
and s_score <60
order by s_score DESC;
50、删除学生编号为“02”的课程编号为“01”的成绩
delete from Score
where s_id='02'
and c_id='01';
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