Mysql classic practice questions 50 questions

The online version of this set of practice questions mostly uses the older mysql version, and I use the Server version: 8.0.15 MySQL

Practice data

Data table--1. Student table Student (SId, Sname, Sage, Ssex)

--SId student number, Sname student name, Sage birth date, Ssex student gender

--2. Course schedule Course (CId, Cname, TId) --CId --Course number, Cname course name, TId teacher number

--3. Teacher table Teacher (TId, Tname)-TId teacher number, Tname teacher name

--4. Score table SC (SId, CId, score) --SId student number, CId course number, score

Create test data

Student table

create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));
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('09' , '张三' , '2017-12-20' , '女');
insert into Student values('10' , '李四' , '2017-12-25' , '女');
insert into Student values('11' , '李四' , '2017-12-30' , '女');
insert into Student values('12' , '赵六' , '2017-01-01' , '女');
insert into Student values('13' , '孙七' , '2018-01-01' , '女');

Course Chart

create table Course(CId varchar(10),Cname nvarchar(10),TId varchar(10))
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');

Teacher table

create table Teacher(TId varchar(10),Tname varchar(10))
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');

Transcript SC

create table SC(SId varchar(10),CId varchar(10),score decimal(18,1))
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

Practice questions

1. Query the information and course scores of students with a higher grade in the "01" course than the "02" course 1.1 Query the situation where the "01" course and the "02" course exist at the same time 1.2 Query the existence of the "01" course but there may be no "02" course Situation (displayed as null when it does not exist) 1.3 Query the situation where "01" course does not exist but "02" course exists
2. Query the student ID, student name and average score of students with an average score greater than or equal to 60 points
3. Query information about students with grades in SC
4. Query the student ID, student name, total number of courses selected, and the total score of all courses (no results are displayed as null) 4.1 Check the information of students with grades
5. Check the number of teachers with the surname "Li"
6. Inquire about the information of the students who have taught "Teacher Zhang"
7. Query information about students who have not completed all courses
8. Query the information of at least one class that has the same class number as the class number "01"
9. Query the information of other students who have the same courses as the students of "01"
10. Query the names of students who have not studied any course taught by "Zhang San"
11. Query the student numbers, names and average grades of students who failed two or more courses
12. Retrieve "01" course score less than 60, in descending order of student information
13. Show the grades and average grades of all students in all courses by average grades from high to low
14. Query the highest score, lowest score and average score of each subject: Displayed in the following form: course ID, course name, highest score, lowest score, average score, passing rate, medium rate, excellent rate, excellent rate passing rate is> = 60, Medium: 70-80, Excellent: 80-90, Excellent:> = 90 The course number and the number of electives are required to be output. The query results are sorted in descending order of number, and if the number is the same, they are sorted in ascending order of course number
15. Sort by the scores of each subject and display the ranking. Keep the position vacancies when the score is repeated
16. Query the student's total score and rank, keep the position vacancy when the total score is repeated 16.1 Query the student's total score and rank, do not keep the rank vacancy when the total score is repeated
17. Count the number of scores in each section of each subject: course number, course name, [100-85], [85-70], [70-60], [60-0] and the percentage
18. Query the records of the top three in each subject
19. Query the number of students selected for each course
20. Find out the student ID and name of students who only take two courses
21. Check the number of boys and girls
22. Query information about students whose name contains "feng"
23. Query the list of same-sex students of the same name and count the number of students with the same name
24. Check the list of students born in 1990
25. Query the average score of each course, the results are sorted in descending order of average grade, when the average grades are the same, they are arranged in ascending order of course number
26. Query the student ID, name and average score of all students whose average score is greater than or equal to 85
27. Query the name and score of students whose course name is "Math" and whose score is less than 60
28. Query all students' courses and scores (there are cases where students have no grades and no courses)
29. Query the name, course name and score of any course with a score above 70
30. Query failed courses
31. Query the student ID and name of the student whose course number is 01 and whose course score is above 80
32. Find the number of students in each course
33. The scores are not repeated. Check the information and scores of the students with the highest grades among the students who take the course taught by Teacher "Zhang San"
34. In the case of duplicate scores, inquire about the information and scores of the students with the highest grades among the students electing the course taught by Teacher "Zhang San"
35. Query the student ID, course ID, and student scores of students with the same grade in different courses
36. Query the top two with the best scores in each skill
37. Count the number of students electing each course (only courses with more than 5 students are counted).
38. Retrieve student IDs for at least two courses
39. Query information about students who have taken all courses
40. Check the age of each student, only calculated by year
41. According to the date of birth, the current month and day <the month and day of the birth year, the age is reduced by one
42. Query students who have a birthday this week
43. Query students who have birthdays next week
44. Query students who have a birthday this month
45. Query students who have birthdays next month 

Reference answer

--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 * from
(select SC.SId, SC.score from SC where SC.CId = '01') as t1 inner join
(select SC.SId, SC.score from SC where SC.CId = '02') as t2 on t1.SId = t2.SId
where t1.score > t2.score

--1.1 查询同时存在" 01 "课程和" 02 "课程的情况

select * from
(select SC.SId, SC.score from SC where SC.CId = '01') as t1 inner join
(select SC.SId, SC.score from SC where SC.CId = '02') as t2 on t1.SId = t2.SId

--1.2 查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )

select * from
(select SC.SId, SC.score from SC where SC.CId = '01') as t1 left join
(select SC.SId, SC.score from SC where SC.CId = '02') as t2 on t1.SId = t2.SId

-- 1.3 查询不存在" 01 "课程但存在" 02 "课程的情况

select * 
from sc
where SId not in (select SId from  sc where CId = '01') 
and CId = '02'

-- 2. 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 t1.sid, t1.sname, t2.avgscore 
from student as t1 inner join (
select sc.sid, avg(sc.score) as avgscore from sc group by sc.sid 
having avgscore >= 60) as t2
on t1.sid = t2.sid

-- 3. 查询在 SC 表存在成绩的学生信息     注意⚠️DISTINCT⚠️关键字

select DISTINCT student.* 
from student, sc
where student.sid = sc.sid 

-- 4. 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(没成绩的显示为null)

select student.sid, student.sname, t1.coursecount, t1.sumscore
from student inner join (
select sc.sid, count(sc.cid) as coursecount, sum(sc.score) as sumscore from sc group by sc.sid) as t1
on student.sid = t1.sid

-- 4.1 查有成绩的学生信息    注意⚠️EXISTS⚠️关键字

select student.* 
from student 
where student.sid in (
select DISTINCT sc.sid from sc)

select *
from student
where EXISTS(select * from sc where student.SId=sc.SId)

-- 5. 查询「李」姓老师的数量

select count(*) 
from teacher
where teacher.Tname like '李%'

-- 6. 查询学过「张三」老师授课的同学的信息

select student.* 
from student, sc 
where student.sid = sc.sid 
and sc.cid in (select cid from course, teacher where course.tid = teacher.tid and Tname = '张三')

-- 同时连接多张表
select student.*
from teacher  ,course  ,student, sc
where teacher.Tname='张三'
and   teacher.TId=course.TId
and   course.CId=sc.CId
and   sc.SId=student.SId

-- 7. 查询没有学全所有课程的同学的信息

-- 这种解法不包括什么课都没选的学生
select student.* from student, (select sid, count(cid) as coursecount from sc group by sid) as t1
where student.sid = t1.sid 
and t1.coursecount<>3

select student.*
from sc ,student
where sc.SId=student.SId
GROUP BY sc.SId
Having count(*)<(select count(*) from course)


-- 利用笛卡尔积可以把什么课都没选的同学查询出来
select DISTINCT student.*
from 
(select student.SId,course.CId
from student,course ) as t1 LEFT JOIN (SELECT sc.SId,sc.CId from sc)as t2 on t1.SId=t2.SId and t1.CId=t2.CId,student
where t2.SId is null
and   t1.SId=student.SId


select student.* from student
where student.sid not in (
select student.sid from sc, student 
where sc.sid = student.sid
group by sid 
having count(*) = (select count(*) from course))

-- 8. 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 student.* 
from sc, student
where sc.CId in (
select CId from sc where SId='01')
and sc.SId = student.SId

-- 9. 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 DISTINCT student.*
from (
select student.SId, t.CId
from student ,(select sc.CId from sc where sc.SId='01') as t)
as t1 LEFT JOIN sc on t1.SId=sc.SId and t1.CId=sc.CId,student
where sc.SId is not null 
and t1.SId=student.SId
and t1.SId <>'01'

-- 10. 查询没学过"张三"老师讲授的任一门课程的学生姓名

 -- solution1
select * 
from student 
where student.SId not in (
select student.SId from (
select student.SId, t.CId from (
select course.CId from course, teacher 
where  course.TId = teacher.TId and teacher.Tname = '张三') as t, student) as t1 
right join sc on t1.SId=sc.SId and t1.CId=sc.CId, student
where t1.SId=student.SId)

-- solution2
select *
from student 
where student.SId not in 
(
    select student.SId
from student left join sc on student.SId=sc.SId 
where EXISTS 
(select *
from teacher ,course
where teacher.Tname='张三'
and   teacher.TId=course.TId
and 	course.CId=sc.CId))

-- 11.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 student.SId, student.Sname, t2.avgscore
from student, (select sc.SId, avg(sc.score) as avgscore from sc group by sc.SId) as t2
where student.SId = t2.SId
and student.SId in (
select t1.SId from
(select * from sc
where sc.score < 60) as t1
group by t1.SId
having count(*) >= 2)

-- 12. 检索" 01 "课程分数小于60，按分数降序排列的学生信息

select student.*, t1.score from student, (
select * from sc 
where sc.CId = '01' and sc.score < 60) as t1
where student.SId = t1.SId
order by t1.score DESC

-- 13. 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 sc.*, t1.avgscore from sc left join
(select sc.SId, avg(sc.score) as avgscore 
from sc group by sc.SId) as t1
on sc.SId = t1.SId
order by t1.avgscore DESC

-- 14. 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 
-- 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 sc.CId, max(sc.score) as '最高分', min(sc.score) as '最低分', avg(sc.score) as '平均分',
count(*) as '选修人数', sum(case when sc.score >= 60 then 1 else 0 end)/count(*) as '及格率',
sum(case when sc.score >= 70 and sc.score < 80 then 1 else 0 end)/count(*) as '中等率',
sum(case when sc.score >= 80 and sc.score < 90 then 1 else 0 end)/count(*) as '优良率',
sum(case when sc.score >= 90 then 1 else 0 end)/count(*) as '优秀率'
from sc 
group by sc.CId
order by count(*) DESC, sc.CId ASC

-- 15. 按各科成绩进行排序，并显示排名，Score 重复时保留名次空缺

SELECT *, RANK() OVER(PARTITION BY sc.cid ORDER BY sc.score DESC)排名
FROM sc;

-- 15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次

SELECT *, DENSE_RANK() OVER(PARTITION BY sc.cid ORDER BY sc.score DESC)排名
FROM sc;

-- 16. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺

SELECT sc.SId, RANK() OVER(ORDER BY sum(sc.score) DESC)排名, sum(sc.score) as sumscore

FROM sc

GROUP BY sc.SId

ORDER BY sumscore DESC;


-- 16.1 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺

SELECT sc.SId, DENSE_RANK() OVER(ORDER BY sum(sc.score) DESC)排名, sum(sc.score) as sumscore

FROM sc

GROUP BY sc.SId

ORDER BY sumscore DESC;


-- 17. 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]，[60-0] 及所占百分比

select sc.CId, sum(case when sc.score >=85 then 1 else 0 end) as num_100_85,
sum(case when sc.score >=70 and sc.score <85 then 1 else 0 end) as num_85_70,
sum(case when sc.score >= 60 and sc.score < 70 then 1 else 0 end) as num_70_60,
sum(case when sc.score < 60 then 1 else 0 end) as num_60_0,
sum(case when sc.score >=85 then 1 else 0 end)/count(*) as p_100_85,
sum(case when sc.score >=70 and sc.score <85 then 1 else 0 end) /count(*) as p_85_70,
sum(case when sc.score >= 60 and sc.score < 70 then 1 else 0 end)/count(*) as p_70_60,
sum(case when sc.score < 60 then 1 else 0 end)/count(*) as p_60_0
from sc 
group by sc.CId

-- 18. 查询各科成绩前三名的记录

SELECT * 

FROM(

	SELECT *, RANK() OVER (PARTITION BY sc.CId ORDER BY sc.score) as r

	FROM sc) as A

WHERE A.r <= 3


-- 19. 查询每门课程被选修的学生数
SELECT sc.CId, COUNT(*)

FROM sc

GROUP BY(sc.CId)


-- 20. 查询出只选修两门课程的学生学号和姓名

SELECT DISTINCT student.SId, student.Sname 

FROM student, (

	SELECT sc.SId, COUNT(*) as a

	FROM sc

	GROUP BY(sc.SId)) as A

WHERE student.SId = A.SId

AND A.a = 2



SELECT Distinct student.Sid, student.Sname

FROM student 

where student.SId in (

SELECT sc.SId 

FROM sc

GROUP BY sc.SId

having count(*)=2)


-- 21. 查询男生、女生人数

SELECT Ssex, count(*)

FROM student

GROUP BY student.Ssex

-- 22. 查询名字中含有「风」字的学生信息

SELECT *

FROM student

WHERE student.sname LIKE '%风%';


-- 23. 查询同名同姓学生名单，并统计同名人数

SELECT Sname, count(*)

FROM student

GROUP BY Sname

HAVING COUNT(*) >1;


-- 24. 查询 1990 年出生的学生名单

SELECT *

FROM student

WHERE sage LIKE '1990-%';

-- 25.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 sc.CId, avg(sc.score) as avgscore

FROM sc

GROUP BY sc.CId

ORDER BY avg(sc.score) DESC, sc.CId

-- 26.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 student.Sid, student.Sname, t.avgscore

FROM student, (

	SELECT sc.SId, avg(sc.score) as avgscore

	FROM sc

	GROUP BY sc.SId) as t

WHERE student.SId = t.SId

AND t.avgscore >= 85

-- 27.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.Sname, t.score

FROM student, (

	SELECT sc.SId, sc.score

	FROM sc 

	WHERE sc.score < 60

	AND sc.CId = (SELECT CId FROM course WHERE course.Cname='数学')) as t

WHERE student.SId = t.SId

-- 28.查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）

SELECT st.*, sc.CId, sc.score

FROM student AS st

LEFT JOIN sc

ON st.SId = sc.SId

ORDER BY st.SId, sc.CId;

-- 29.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.Sname, course.Cname, sc.score

FROM student, course, sc

WHERE student.SId = sc.SId

AND course.CId = sc.CId

AND sc.score > 70

ORDER BY sc.CId

-- 30.查询不及格的课程

SELECT sc.CId, sc.score

FROM sc

WHERE sc.score <60

ORDER BY sc.CId;

-- 31.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 student.SId, student.Sname 

FROM student, sc

WHERE student.SId = sc.SId

AND sc.CId = '01'

AND sc.score > 80

-- 32.求每门课程的学生人数

SELECT sc.CId, count(sc.SId)

FROM sc

GROUP BY sc.CId

-- 33.成绩不重复，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 student.*, sc.score, sc.CId 

FROM student, sc

WHERE sc.CId = (SELECT course.CId 

FROM course, teacher

WHERE course.TId = teacher.TId

AND teacher.Tname = '张三')

AND student.SId = sc.SId

ORDER BY sc.score DESC

LIMIT 1

-- 34.成绩有重复的情况下，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 student.*, sc.score, sc.CId, DENSE_RANK() OVER (ORDER BY sc.score DESC)排名 

FROM student, sc

WHERE sc.CId = (SELECT course.CId 

FROM course, teacher

WHERE course.TId = teacher.TId

AND teacher.Tname = '张三')

AND student.SId = sc.SId) as t

WHERE t.排名='1'

-- 35.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 sc.SId, sc.CId, sc.score

FROM sc

WHERE sc.score in (

SELECT score FROM(

SELECT sc.score, count(sc.score) as count_people

FROM sc

GROUP BY sc.score) A

WHERE A.count_people > 1) 


SELECT s,c,score

FROM

(

  SELECT max(score),avg(score),COUNT(score),student.s,c,score

  FROM student

  LEFT JOIN sc

  ON student.s=sc.s

  GROUP BY student.s

  HAVING max(score)=avg(score) AND COUNT(score)>=2

) A;


-- 36.查询每门功成绩最好的前两名

SELECT * 
FROM (SELECT sc.SId, sc.CId, sc.score, row_number() over (PARTITION BY sc.CId ORDER BY sc.score DESC)排名
FROM sc
ORDER BY sc.score DESC) A
WHERE 排名 <= 2
ORDER BY A.CId, A.排名


-- 37.统计每门课程的学生选修人数（超过 5 人的课程才统计)

SELECT * 

FROM (

SELECT sc.CId, count(sc.SId) as count_people

FROM sc

GROUP BY sc.CId) A

WHERE A.count_people > 5




SELECT sc.CId,COUNT(sc.CId)

FROM sc

GROUP BY sc.CId

HAVING COUNT(sc.CId)>5 ;


-- 38.检索至少选修两门课程的学生学号

SELECT sc.SId, COUNT(sc.SId)

FROM sc

GROUP BY sc.SId

HAVING COUNT(sc.SId) >= 2 

-- 39.查询各学生的年龄，只按年份来算

SELECT SId, Sname, (year(curdate())-year(Sage)) as age 

FROM student

ORDER BY age


-- 40.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 SId, Sname,timestampdiff(year,Sage,curdate())年龄

FROM student

ORDER BY 年龄;

-- 41. 查询本周过生日的学生

SET @day =8-dayofweek(curdate());


SELECT *

FROM student

WHERE date_format(Sage, '%m%d') 

BETWEEN date_format(curdate(),'%m%d') 

AND date_format (date_add(curdate(),interval @day day), '%m%d');


-- 42.查询下周过生日的学生

set @day =9-dayofweek(curdate());


SELECT *

FROM student

WHERE date_format(sage, '%m%d') 

BETWEEN date_format (date_add(curdate(),interval @day day), '%m%d')

AND date_format (date_add(curdate(),interval @day+6 day), '%m%d');

-- 43.查询本月过生日的学生

SELECT *

FROM student

WHERE date_format(Sage,'%m')=date_format(curdate(),'%m');


-- 44.查询下月过生日的学生

SELECT *

FROM student

WHERE date_format(Sage,'%m')=date_format(date_add(curdate(),interval 1 month),'%m');