Day05 05-MySQL实战练习及答案

第十八章 MySQL实战练习

MySQL的实战练习主要目标是提升初学者对MySQL的语法、语感、手法和手感，增强大家对SQL语句的热爱度。

大数据开发、数据仓库开发、数据分析师或者数据治理等大数据相关岗位，其实更多的时候都是在对SQL进行拿捏，所以建议大家有时间一定一定要把夯实SQL基础，下面的练习题及答案仅供大家参考，大家可以再去衍生想想，如何去查看SQL的执行计划？如何提升SQL查询性能？

18.1 数据准备

18.1.1 数据库表DDL

-- 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`)
);

18.1.2 数据库表DML

-- 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);

18.2 实战练习题目及参考答案

题目及答案仅供参考，可以按照自己的合理的理解进行作答，建议大家有时间可以多练习其它更多的SQL场景。

-- 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 a.s_id 
from 
(
select *
from score
where c_id = '01'
) a
left join 
(
select *
from score
where c_id = '02'
) b
 on b.s_id =a.s_id 
 where a.s_score > b.s_score or b.s_score is null
;

select stu.*,c.*
from student stu
join score a on a.c_id = '01' and a.s_id= stu.s_id
left join score b on b.c_id = '02' and b.s_id= stu.s_id
join score c on c.s_id= stu.s_id
where a.s_score > b.s_score or b.s_score is null
;

-- 2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数:
select stu.*,c.s_score
from student stu
join score a on a.c_id = '02' and a.s_id= stu.s_id
left join score b on b.c_id = '01' and b.s_id= stu.s_id
join score c on c.s_id= stu.s_id
where a.s_score >= b.s_score or b.s_score is null
;

-- 3、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.s_id,stu.s_name,avg(a.s_score) as avgscore
from score a
join student stu on a.s_id = stu.s_id
group by a.s_id,stu.s_name
having avgscore >= 60
;

-- 4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩:(包括有成绩的和无成绩的)
select 
a.s_id,stu.s_name,avg(a.s_score) as avgscore
from score a
join student stu on a.s_id = stu.s_id
group by a.s_id,stu.s_name
having avgscore < 60
union all
select stu.s_id,stu.s_name,NULL as avgscore
from student stu
left join score a on stu.s_id = a.s_id
where a.s_score is null
;


select stu.s_id,stu.s_name,NULL as avgscore
from student stu
where not exists (select 1 from score a where a.s_id = stu.s_id)
;

select stu.s_id,stu.s_name,NULL as avgscore
from student stu
left join score a on stu.s_id = a.s_id
where a.s_score is null
;

select stu.s_id,stu.s_name,NULL as avgscore
from student stu
where stu.s_id not in (select s_id from score )
;

-- 5、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:
select 
stu.s_id,stu.s_name,count(a.s_score) as totalSubjects,sum(a.s_score) as sumScores
from student stu
left join score a on a.s_id = stu.s_id
group by stu.s_id,stu.s_name
;

select 
stu.s_id,stu.s_name,
count(a.s_score) over(partition by stu.s_id) as totalSubjects,
sum(a.s_score) over(partition by stu.s_id) as sumScores
from student stu
left join score a on a.s_id = stu.s_id
;

-- 6、查询"李"姓老师的数量:
select count(1)
from teacher
where t_name like '李%'
;

-- 7、查询学过"张三"老师授课的同学的信息:
select distinct stu.*
from student stu
join score a on a.s_id = stu.s_id
join course b on b.c_id = a.c_id
join teacher c on c.t_id =b.t_id 
where c.t_name = '张三'
;

select stu.*
from student stu
where exists (select 1 from score a,course b,teacher c where c.t_name='张三' and  c.t_id = b.t_id and b.c_id = a.c_id and stu.s_id = a.s_id)
;

select stu.*
from student stu
join course b on b.c_id = a.c_id
join teacher c on c.t_name = '张三' and c.t_id =b.t_id 
left semi join score a on a.s_id = stu.s_id
;


-- 8、查询没学过"张三"老师授课的同学的信息:
select stu.*,cs.c_course,sc.s_score
from student stu
join teacher ter on ter.t_name = '张三'
join course cs on ter.t_id = cs.t_id 
left join score sc on sc.s_id = stu.s_id and sc.c_id = cs.c_id
where sc.s_score is null
;

select stu.s_id,stu.s_name
from student stu
join teacher c on c.t_name = '张三' 
join course b on c.t_id= b.t_id
left join score a on b.c_id = a.c_id and a.s_id = stu.s_id
group by stu.s_id,stu.s_name
having sum(case when a.s_score is null then 0 else 1 end ) = 0
;

select stu.*
from student stu
where not exists (select 1 from score a,course b,teacher c where c.t_name='张三' and  c.t_id = b.t_id and b.c_id = a.c_id and stu.s_id = a.s_id)
;


-- 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息:
select stu.*
from student stu
join score a on a.s_id =stu.s_id and a.c_id = '01' 
where exists (select 1 from score b where b.c_id = '02' and stu.s_id = b.s_id)
;


select stu.*
from student stu,score a,score b 
where stu.s_id = a.s_id and stu.s_id = b.s_id and a.c_id = '01' and b.c_id = '02'
;

select stu.s_id,stu.s_name
from student stu
join score a on stu.s_id =a.s_id 
where a.c_id = '01' or a.c_id = '02'
group by stu.s_id,stu.s_name
having count(1) = 2
;

select stu.s_id,stu.s_name
from student stu
join score a on stu.s_id =a.s_id 
where a.c_id in (1,2)
group by stu.s_id,stu.s_name
having count(1) = 2
;


-- 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息:
select stu.*
from student stu
join score a on a.s_id =stu.s_id and a.c_id = '01' 
where not exists (select 1 from score b where b.c_id = '02' and stu.s_id = b.s_id)
;

select stu.s_id,stu.s_name
from student stu
join score sc on sc.c_id= '01' and sc.s_id = stu.s_id
left join score sc1 on sc1.c_id= '02' and sc1.s_id = sc.s_id
where sc1.s_score is null
;

-- 11、查询没有学全所有课程的同学的信息:
select distinct stu.*
from student stu
join course a 
left join score b on b.s_id = stu.s_id and b.c_id = a.c_id 
where b.s_score is null
;

-- 12、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 stu.*
from student stu
join score a on a.s_id = stu.s_id
where stu.s_id <> '01' and a.c_id in (
select c_id from score where s_id = '01')
;

select distinct stu.*
from student stu
join score a on a.s_id = stu.s_id and a.s_id = '01'
join score b on b.c_id = a.c_id
where stu.s_id <> '01'
;


-- 13、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 stu.s_id,stu.s_name,stu.s_birth,stu.s_sex
from student stu
join 
(
select stu.s_id as stid,sc1.s_id as scid,case when stu.s_id is null then sc1.s_id else stu.s_id end as all_id
from student stu
join (
select sc.c_id
from score sc
where sc.s_id = '01' and sc.c_id <> '01'
) aa
full outer join score sc1 on sc1.c_id = aa.c_id and sc1.s_id = stu.s_id
) a on a.all_id = stu.s_id
group by stu.s_id,stu.s_name,stu.s_birth,stu.s_sex
having sum(case when stid is null or scid is null then 1 else 0 end) = 0
;

select student.*,tmp1.course_id 
from student
join (
select s_id ,concat_ws('|', collect_set(c_id)) course_id 
from score
where s_id <> '01'
group by s_id)tmp1
  on student.s_id = tmp1.s_id
join (
select concat_ws('|', collect_set(c_id)) course_id2
from score  
where s_id='01' and c_id <> '01')tmp2
on tmp1.course_id = tmp2.course_id2;


-- 14、查询没学过"张三"老师讲授的任一门课程的学生姓名:
select *
from student stu
where stu.s_id not in (
select c.s_id 
from course a,teacher b,score c 
where b.t_name = '张三' and a.t_id = b.t_id and c.s_id = stu.s_id and c.c_id = a.c_id
)
;

select stu.*
from student stu
join teacher a on a.t_name = '张三'
join course b on b.t_id = a.t_id
left join score c on c.c_id = b.c_id and c.s_id = stu.s_id
where c.s_score is null
;


-- 15、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 
*
from student stu 
join score a on a.s_id = stu.s_id
where a.s_score < 60
;

select 
stu.s_id,
stu.s_name,round(avg(b.s_score),2) as avgscore
from student stu 
join score a on a.s_id = stu.s_id
join score b on b.s_id = stu.s_id
where a.s_score < 60
group by stu.s_id,stu.s_name
having count(1) >= 2
;

-- 16、检索"01"课程分数小于60，按分数降序排列的学生信息:
select *
from student stu
join score a on a.s_id = stu.s_id
where a.c_id = '01' and a.s_score < 60
order by a.s_score desc
;

-- 17、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 *
from score b
join 
(
select a.s_id,round(avg(a.s_score),2) as avgscore
from score a
group by a.s_id
order by avgscore desc
) d on d.s_id = b.s_id
;

select *,
round(avg(a.s_score) over(partition by a.s_id),2) as avgscore
from score a
order by avgscore desc,a.s_score desc
;


-- 18.查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率:
-- 及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
select 
b.c_id,
b.c_course,
max(a.s_score) as maxscore,
min(a.s_score) as minscore,
round(avg(a.s_score),2) as avgscore,
round(sum(case when a.s_score >=60 then 1 else 0 end ) / count(1) * 100,2) as `及格率`,
round(sum(case when a.s_score between 70 and 79 then 1 else 0 end ) / count(1) * 100,2) as `中等率`,
round(sum(case when a.s_score between 80 and 89 then 1 else 0 end ) / count(1) * 100,2) as `优良率`,
round(sum(case when a.s_score >=90 then 1 else 0 end ) / count(1) * 100,2) as `优秀率`
from score a
join course b on b.c_id = a.c_id
group by b.c_id,b.c_course
;

-- 19、按各科成绩进行排序，并显示排名:– row_number() over()分组排序功能
select *,
row_number() over(partition by c_id sort by s_score desc)
from score
;

-- 20、查询学生的总成绩并进行排名:
select s_id,sum(s_score) as sumScores
from score
group by s_id
order by sumscores desc;

-- 21、查询不同老师所教不同课程平均分从高到低显示:
select t_id,a.c_id,round(avg(s_score),2) as avgscore
from score a
join course b on b.c_id = a.c_id
group by t_id,a.c_id
order by t_id,avgscore desc 
;

-- 22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩:
select * from 
(
select *,
row_number() over(partition by c_id sort by s_score desc) as rm
from score
) a
where a.rm between 2 and 3
;

-- 23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比
select c_id,
sum(case when s_score >= 85 then 1 else 0 end) as 85score,
sum(case when s_score between 70 and 84 then 1 else 0 end) as 70score,
sum(case when s_score between 60 and 69 then 1 else 0 end) as 60score,
sum(case when s_score < 60 then 1 else 0 end) as 59score,
count(1) as totalstu
from score
group by c_id
;

-- 24、查询学生平均成绩及其名次:
select *,
row_number() over(sort by a.avgscore desc) as rm
from (
select 
s_id,
round(avg(s_score),2) as avgscore
from score
group by s_id ) a
;

-- 25、查询各科成绩前三名的记录三个语句
select * from 
(
select *,
row_number() over(partition by c_id sort by s_score desc) as rm,
rank() over(partition by c_id sort by s_score desc) as rk,
dense_rank() over(partition by c_id sort by s_score desc) as drk
from score
) a
where a.rm < 4
;

-- 26、查询每门课程被选修的学生数:
select c_id,count(1) as totalstu
from score
group by c_id
;

-- 27、查询出只有两门课程的全部学生的学号和姓名:
select stu.s_id,stu.s_name
from student stu
join score a on a.s_id = stu.s_id
group by  stu.s_id,stu.s_name
having count(1) = 2
;

-- 28、查询男生、女生人数:
select s_sex,count(1) as totalstu
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、查询同名同性学生名单，并统计同名人数:
select s_name,s_sex,count(1) as totalstu
from student
group by s_name,s_sex
having totalstu > 1
;

-- 31、查询1990年出生的学生名单:
select * 
from student 
where s_birth like '1990%'
; 

-- 32、查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列:
select c_id,round(avg(s_score),2) as avgscore
from score
group by c_id
order by avgscore desc,c_id asc
;

-- 33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩:
select s_id,avg(s_score) as avgscore
from score
group by s_id
having avgscore >= 85
;

-- 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 stu.s_name,a.s_score
from score a
join course b on b.c_course = '数学' and b.c_id = a.c_id
join student stu on stu.s_id = a.s_id
where a.s_score < 60
;

-- 35、查询所有学生的课程及分数情况:
select *
from student stu
join course a
left join score b on b.s_id = stu.s_id and b.c_id = a.c_id
;

-- 36、查询任何一门课程成绩在70分以上的学生姓名、课程名称和分数:
select *
from student stu
join score a on a.s_id = stu.s_id
join course b on b.c_id = a.c_id
where a.s_score >=70
;

-- 37、查询课程不及格的学生:
select *
from student stu
join score a on a.s_id = stu.s_id
where a.s_score < 60
;

-- 38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名:
select *
from score
where c_id = '01' and s_score >= 80
;

-- 39、求每门课程的学生人数:
select c_id,count(1) as totalstu
from score
group by c_id
;

-- 40、查询选修"张三"老师所授课程的学生中，成绩最高的学生信息及其成绩:
select *
from (
select a.*,
dense_rank() over (partition by a.c_id sort by a.s_score desc) drk 
from score a
join course b on b.c_id =a.c_id
join teacher c on c.t_id = b.t_id
where c.t_name = '张三'
) aa
where aa.drk = 1;


-- 41、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:
SELECT distinct b.s_id,b.c_id,b.s_score 
FROM score a,score b 
WHERE a.c_id != b.c_id AND a.s_score = b.s_score and a.s_id = b.s_id
;

select * from 
score a
join (
select s_id,s_score
from score
group by s_id,s_score
having count(1) > 1
) b on b.s_id = a.s_id and b.s_score = a.s_score
;

-- 42、查询每门课程成绩最好的前三名:
select * 
from (
select *,
dense_rank() over(partition by c_id sort by s_score desc) drk
from score
) a 
where a.drk < 4
;

-- 43、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列，若人数相同，按课程号升序排列
SELECT c_id,COUNT(*) AS total 
FROM score 
GROUP BY c_id 
HAVING total>5 
ORDER BY total desc,c_id ASC;

-- 44、检索至少选修两门课程的学生学号:
SELECT s_id,COUNT(*) AS sel 
FROM score 
GROUP BY s_id 
HAVING sel>=2;

-- 45、查询选修了全部课程的学生信息:
select stu.s_id,stu.s_name
from student stu
join course a
left join score b on b.c_id = a.c_id and b.s_id = stu.s_id
group by stu.s_id,stu.s_name
having sum(case when b.s_score is null then 1 else 0 end) = 0
;


-- 46、查询各学生的年龄(周岁):
-- 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
SELECT s_birth,(year(current_date())-year(s_birth) - 
                (CASE 
	WHEN month(current_date())>month(s_birth) THEN 0 
	when month(current_date())= month(s_birth) and day(current_date())>=day(s_birth) then 0 ELSE 1 END)) AS age
        FROM student;
		

-- 47、查询本周过生日的学生:
SELECT * FROM student WHERE weekofyear(s_birth)=weekofyear(current_date());

SELECT weekofyear(current_date());

-- 48、查询下周过生日的学生:
SELECT * FROM student WHERE weekofyear(s_birth)=weekofyear(current_date()) + 1;

-- 49、查询本月过生日的学生:
SELECT * FROM student WHERE MONTH(current_date()) =MONTH(s_birth);

-- 50、查询12月份过生日的学生:
SELECT * FROM student WHERE 12=MONTH(s_birth);