50 MySQL exercises + Answers

MySQL Exercises + answer

50 Taoist classics SQL The answer to the exercise

Data sheet introduction

• 1. learn ⽣ surface Student(SId,Sname,Sage,Ssex)

  • SId learn ⽣ Number

  • Sname learn ⽣ full name

  • Sage Out ⽣ year ⽉

  • Ssex learn ⽣ Gender

• 2. The curriculum Course(CId,Cname,TId)

  • CId Course number

  • Cname Course name

  • TId Teacher number

• 3. Teachers list Teacher(TId,Tname)

  • TId Teacher number

  • Tname Teacher's name

• 4. League tables SC(SId,CId,score)

  • SId learn ⽣ Number

  • CId Course number

  • score fraction

Create table statement

• learn ⽣ surface Student

  create table Student(
      SId varchar(10),
      Sname varchar(10),
      Sage datetime,
      Ssex varchar(10)
  ); 
  

• The curriculum Course

  create table Course(
      CId varchar(10),
      Cname varchar(10),
      TId varchar(10)
  );
  

• Teachers list Teacher

  create table Teacher(
      TId varchar(10),
      Tname varchar(10)
  );
  

• League tables SC

  create table SC(
      SId varchar(10),
      CId varchar(10),
      score decimal(18,1)
  );
  

insert data

• learn ⽣ surface Student

  --  Student list  Student
  insert into Student values('01' , ' Zhao Lei ' , '1990-01-01' , ' male '); 
  insert into Student values('02' , ' Qian Dian ' , '1990-12-21' , ' male '); 
  insert into Student values('03' , ' Sun Feng ' , '1990-12-20' , ' male '); 
  insert into Student values('04' , ' Li Yun ' , '1990-12-06' , ' male '); 
  insert into Student values('05' , ' Zhou Mei ' , '1991-12-01' , ' Woman '); 
  insert into Student values('06' , ' Wu Lan ' , '1992-01-01' , ' Woman '); 
  insert into Student values('07' , ' Zheng Zhu ' , '1989-01-01' , ' Woman '); 
  insert into Student values('09' , ' Zhang San ' , '2017-12-20' , ' Woman '); 
  insert into Student values('10' , ' Li Si ' , '2017-12-25' , ' Woman '); 
  insert into Student values('11' , ' Li Si ' , '2012-06-06' , ' Woman '); 
  insert into Student values('12' , ' Zhao Liu ' , '2013-06-13' , ' Woman '); 
  insert into Student values('13' , ' Sun Qi ' , '2014-06-01' , ' Woman '); 
  

• The curriculum Course

  --  Families, ⽬ surface  Course 
  insert into Course values('01' , ' Chinese language and literature ' , '02'); 
  insert into Course values('02' , ' mathematics ' , '01'); 
  insert into Course values('03' , ' English ' , '03');
  

• Teachers list Teacher

  --  Teachers list  Teacher 
  insert into Teacher values('01' , ' Zhang San '); 
  insert into Teacher values('02' , ' Li Si '); 
  insert into Teacher values('03' , ' Wang Wu '); 
  

• League tables SC

  --  League tables  SC 
  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);
  

Exercise questions

1. Inquire about " 01 “ Course ⽐” 02 " Course results ⾼ Science ⽣ Information and course scores

select  ttt1.SId
        ,ttt1.chinese_score
        ,ttt1.math_score
        ,ttt2.SName
from(
    select  tt1.SId
            ,ifnull(tt1.chinese_score,0) as chinese_score
            ,ifnull(tt1.math_score,0) as math_score
    from
    (
        select  t1.SId
                ,t1.score as chinese_score
                ,t2.score as math_score
        from(
            select  SId
                    ,CId
                    ,score
            from SC 
            where CId = '01'
        ) t1
        left join (
            select  SId
                    ,CId
                    ,score
            from SC 
            where CId = '02'
        ) t2
        on t1.SId = t2.SId
        union 
        select  t2.SId
                ,t1.score as chinese_score
                ,t2.score as math_score
        from(
            select  SId
                    ,CId
                    ,score
            from SC 
            where CId = '01'
        ) t1
        right join (
            select  SId
                    ,CId
                    ,score
            from SC 
            where CId = '02'
        ) t2
        on t1.SId = t2.SId
    ) tt1
    where if(tt1.chinese_score is null,0,tt1.chinese_score) > ifnull(tt1.math_score,0)
) ttt1
left join Student ttt2
on ttt1.SId = ttt2.SId;

2. Queries exist at the same time " 01 “ Courses and ” 02 " Course situation

select  tt1.SId
        ,tt2.SName
        ,tt2.SAge
        ,tt2.SSex
from(
    select  t1.SId
    from(
        select  SId
        from SC 
        where CId = '01'
    ) t1
    join (
        select  SId
        from SC 
        where CId = '02'
    ) t2
    on t1.SId = t2.SId
) tt1 left join Student tt2 on tt1.SId = tt2.SId;

3. Query exists " 01 “ The course may not exist ” 02 " Course situation ( If it does not exist, it will be displayed as null )

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

4. Query does not exist " 01 “ Course but there is ” 02 " Course situation

select  t1.SId
        ,t2.SId
from(
    select  SId
    from SC 
    where CId = '01'
) t1
right join (
    select  SId
    from SC 
    where CId = '02'
) t2
on t1.SId = t2.SId;

5. Check the grade average ⼤ Is equal to 60 The study of students with different grades ⽣ Numbering and learning ⽣ Name and average score

select  t1.SId
        ,t2.SName
        ,t1.avg_score
from(
    select  SId
            ,avg(score) as avg_score
    from SC
    group by SId
    having avg_score>=60
) t1 left join Student t2
on t1.SId = t2.SId;

6. The query in SC There are academic achievements in the table ⽣ Information

select  SId
        ,SName
from Student 
where SId in (
    select  distinct SId
    from SC
);

7. Check all students' learning ⽣ Number 、 learn ⽣ full name 、 The total number of selected courses 、 Total grade of all courses ( No results are shown as null )

select  t1.SId
        ,t1.SName
        ,t2.ccnt
        ,t2.sum_score
from Student t1
left join (
    select  SId
            ,count(CId) ccnt
            ,sum(score) sum_score
    from SC
    group by SId
) t2 on t1.SId = t2.SId;

8. Inquire about 「 Li 」 surname ⽼ Number of divisions

select  ' Surname Li ' as col1
        ,count(*) as cnt
from Teacher
where Tname like ' Li %';

9. I have learned to query 「 Zhang San 」⽼ Information about the students taught by the teacher

select  t1.SId
        ,t2.SName
from (
    select  SId
    from SC
    where CId = (
        select  CId
        from Course
        where TId = (
            select  TId
            from Teacher
            where TName = ' Zhang San '
        )
    )
) t1 left join Student t2
on t1.SId = t2.SId;

select  SId
        ,SName
from Student
where SId in (
    select  SId
    from SC
    where CId = (
        select  CId
        from Course
        where TId = (
            select  TId
            from Teacher
            where TName = ' Zhang San '
        )
    )
);

10. Check the information of students who have not learned all the courses

select  SId
        ,SName
from Student
where SId not in (
    select  SId
    from (
        select  SId
        ,count(CId) as cnt
        from SC
        group by SId
        having cnt = (
            select  count(CId)
            from Course
        )
    ) t1
);

11. Inquire about ⾄ There is little ⼀⻔ The class and student number are " 01 " Of the students who learn the same information

select  t1.SId
        ,t2.SName
from (
    select  distinct SId 
    from SC
    where SId != '01' 
    and CId in (
        select  CId
        from SC
        where SId = '01'
    )
) t1 left join Student t2
on t1.SId = t2.SId;

12. Query and " 01 " The course of study of No Exactly the same information from other students

select  SId
        ,SName
from Student
where SId in (
    select  t1.SId
    from (
        select  SId
                ,count(CId) as cnt
        from SC
        where SId != '01' 
        and CId in (
            select  CId
            from SC
            where SId = '01'
        ) group by SId
        having cnt = (
            select  count(CId)
            from SC
            where SId = '01'
        )
    ) t1 join (
        select  SId
                ,count(CId) as cnt
        from SC
        where SId != '01'
        group by SId
    ) t2 on t1.SId = t2.SId and t1.cnt = t2.cnt
);

13. I didn't learn how to query " Zhang San "⽼ The teacher teaches ⼀⻔ Course learning ⽣ full name

select  SId
        ,SName
from Student
where SId not in (
    select  distinct
        SId
    from SC
    where CId in (
        select  CId
        from Course
        where TId in (
            select  TId
            from Teacher
            where TName = ' Zhang San '
        )
    )
);

14. Query two ⻔ The student number of students who fail the course or above , Name and average score

select  t1.SId
        ,t2.SName
        ,t1.avg_score
from (
    select  SId
            ,count(CId) as cnt
            ,avg(score) as avg_score
    from SC
    where score <60
    group by SId
    having cnt >= 2
) t1 left join Student t2
on t1.SId = t2.SId;

15. retrieval " 01 " Course grade ⼩ On 60, In descending order of scores ⽣ Information

select  t1.SId
        ,t2.SName
        ,t1.score
from (
    select  SId
            ,score
    from SC
    where CId = '01'
    and score < 60
) t1 left join Student t2
on t1.SId = t2.SId
order by t1.score desc;

16. From... On average ⾼ To low shows all learning ⽣ Grades and GPA of all courses

select  t1.SId
        ,t1.CId
        ,t1.score
        ,t2.avg_score
from SC t1
left join (
    select  SId
            ,round(avg(score),2) as avg_score
    from SC
    group by SId
) t2 on t1.SId = t2.SId
order by t2.avg_score desc;

17. Inquire about the results of each subject ⾼ branch 、 Minimum and average points ： Show as follows ： Course ID, Course name, most ⾼ branch , Lowest score , average , pass rate , Medium rate , Excellent rate , Excellence rate Pass is >=60, The average is ：70-80, Good is ：80-90, Excellence is ：>=90 It is required to output the course number and elective courses ⼈ Count , The query result is displayed by ⼈ The numbers are arranged in descending order , if ⼈ The same number , In ascending order of course number

select  t1.CId
        ,t1.max_score
        ,t1.min_score
        ,t1.avg_score
        ,t1.pass_percent
        ,t1.med_percent
        ,t1.good_percent
        ,t1.best_percent
from(
    select  CId
            ,max(score) as max_score
            ,min(score) as min_score
            ,avg(score) as avg_score
            ,concat(round(sum(if(score>=60,1,0)) * 100/count(SId),2),'%') as pass_percent
            ,concat(round(sum(if(score>=70 and score < 80,1,0)) * 100/count(SId),2),'%') as med_percent
            ,concat(round(sum(if(score>=80 and score < 90,1,0)) * 100/count(SId),2),'%') as good_percent
            ,concat(round(sum(if(score>=90 ,1,0)) * 100/count(SId),2),'%') as best_percent
            ,count(SId) as cnt
    from SC
    group by CId
) t1 left join Course t2
on t1.CId = t2.CId
order by t1.cnt desc,t1.CId;

18. Enter according to the average score of each subject ⾏ Sort , And show ranking , Score Keep the vacancy when repeat

1 2 2 4 5 6

set @i := 0;
set @j := 0;
set @avg_score_front := 0;
set @avg_score_last := 0;
select  tt1.CId
        ,tt1.avg_score
        ,tt1.dense_rk
from (
    select  t1.CId
            ,t1.avg_score
            ,@j := @j + 1
            ,@avg_score_front := t1.avg_score
            ,if(@avg_score_front = @avg_score_last,@i,@i := @j) as rk
            ,@avg_score_last := @avg_score_front
    from 
    (
        select  CId
                ,round(avg(score),2) as avg_score
        from SC
        group by CId
        order by avg_score desc
    ) t1
) tt1;

19. Enter according to the average score of each subject ⾏ Sort , And show ranking , Score There is no vacancy when repeating

1 2 2 3 4 5 6

set @i := 0;
set @avg_score_front := 0;
set @avg_score_last := 0;
select  tt1.CId
        ,tt1.avg_score
        ,tt1.dense_rk
from (
    select  t1.CId
            ,t1.avg_score
            ,@avg_score_front := t1.avg_score
            ,if(@avg_score_front = @avg_score_last,@i,@i := @i + 1) as dense_rk
            ,@avg_score_last := @avg_score_front
    from 
    (
        select  CId
                ,round(avg(score),2) as avg_score
        from SC
        group by CId
        order by avg_score desc
    ) t1
) tt1;

20. Inquiry ⽣ The total score of , Go in parallel ⾏ ranking , Keep the position vacancy when the total score is repeated

set @i:=0;
set @j:=0;
set @sum_score_front:=0;
set @sum_score_back:=0;
select  tt1.SId
        ,tt1.sum_score
        ,tt1.rk
from (
    select  t1.SId
            ,t1.sum_score
            ,@j := @j + 1
            ,@sum_score_front := t1.sum_score
            ,if(@[email protected]_score_back,@i,@i:[email protected]) as rk
            ,@sum_score_back := @sum_score_front
    from (
        select  SId
                ,sum(score) as sum_score
        from SC
        group by SId
        order by sum_score desc
    ) t1
) tt1;

21. Inquiry ⽣ The total score of , Go in parallel ⾏ ranking , If the total score is repeated, no vacancy will be reserved

set @i:=0;
set @sum_score_front:=0;
set @sum_score_back:=0;
select  tt1.SId
        ,tt1.sum_score
        ,tt1.rk
from (
    select  t1.SId
            ,t1.sum_score
            ,@sum_score_front := t1.sum_score
            ,if(@[email protected]_score_back,@i,@i:[email protected] + 1) as rk
            ,@sum_score_back := @sum_score_front
    from (
        select  SId
                ,sum(score) as sum_score
        from SC
        group by SId
        order by sum_score desc
    ) t1
) tt1;

22. Count the scores of all subjects and grades ⼈ Count ： Course number , Course name ,[100-85],[85-70],[70-60],[60-0] And the percentage ⽐

select  t1.CId
        ,t2.CName
        ,t1.85to100_cnt
        ,t1.85to100_cnt_percent
        ,t1.70to85_cnt
        ,t1.70to85_cnt_percent
        ,t1.60to70_cnt
        ,t1.60to70_cnt_percent
        ,t1.0to60_cnt
        ,t1.0to60_cnt_percent
from(
    select  CId
            ,sum(if(score>=85 and score<=100,1,0)) as 85to100_cnt
            ,round(sum(if(score>=85 and score<=100,1,0))/count(SId),2) as 85to100_cnt_percent
            ,sum(if(score>=70 and score<=85,1,0)) as 70to85_cnt
            ,round(sum(if(score>=70 and score<=85,1,0))/count(SId),2) as 70to85_cnt_percent
            ,sum(if(score>=60 and score<=70,1,0)) as 60to70_cnt
            ,round(sum(if(score>=60 and score<=70,1,0))/count(SId),2) as 60to70_cnt_percent
            ,sum(if(score>=0 and score<=60,1,0)) as 0to60_cnt
            ,round(sum(if(score>=0 and score<=60,1,0))/count(SId),2) as 0to60_cnt_percent
    from SC
    group by CId
)t1 left join Course t2 
on t1.CId = t2.CId;

23. Check the records of the top three students in each subject

--  Within the group TopN

24. Query each ⻔ The course is an elective course ⽣ Count

select  CId
        ,count(SId) as cnt
from SC
group by CId;

25. Only two elective courses are found ⻔ Course learning ⽣ Student number and name

select  SId
        ,SName
from Student
where SId in (
    select  t1.SId
    from (
        select  SId
                ,count(CId) as cnt
        from SC
        group by SId
        having cnt = 2
    ) t1
);

26. Inquiry man ⽣、⼥⽣⼈ Count

select  SSex
        ,count(SId) as cnt
from Student
group by SSex;

27. The query name contains 「⻛」 Word learning ⽣ Information

-- like
select  SId
        ,SName
from Student
where SName like '% wind %';

-- re
select  SId
        ,SName
from Student
where SName rlike '.* wind .*';

28. Query homonymy ⽣ list , And statistics of the same name ⼈ Count

select  SName
        ,count(SId) as cnt
from Student
group by SName
having cnt>1;

29. Inquire about 1990 New year's day ⽣ Science ⽣ list

select  SId
        ,SName
        ,SAge
from Student 
where year(SAge) = '1990';

30. Query each ⻔ The average grade of the course , The results are in descending order of average score , The average is the same , In ascending order of course number

select  CId
        ,round(avg(score),2) as avg_score
from SC
group by CId
order by avg_score desc,CId;

31. Check the grade average ⼤ Is equal to 85 All my studies ⽣ The student id 、 Name and average score

select  t1.SId
        ,t2.SName
        ,t1.avg_score
from (
    select  SId
            ,round(avg(score),2) as avg_score
    from SC
    group by SId
    having avg_score>=85
) t1 left join Student t2
on t1.SId = t2.SId;

32. Query the course name as 「 mathematics 」, And the score is lower than 60 Science ⽣ Name and score

select  t1.SId
        ,t2.SName
        ,t1.score
from (
    select  SId
            ,score
    from SC
    where CId in (
        select  CId
        from Course
        where CName = ' mathematics '
    )
) t1 left join Student t2
on t1.SId = t2.SId;

33. Query all learning ⽣ Courses and scores （ Existentialism ⽣ No results , No class selection ）

select  t1.SId
        ,t1.SName
        ,t2.CId
        ,t3.CName
        ,t2.score
from Student t1
left join SC t2
on t1.SId = t2.SId
left join Course t3
on t2.CId = t3.CId
order by SId;

34. Query any ⼀⻔ Course grades are 70 Score the above names 、 Course name and score

--  As long as one subject exceeds 70 branch , Others do not exceed 70 Our subjects also need to be displayed 
select  t1.SId
        ,t1.SName
        ,t3.CName
        ,t2.score
from(
    select  SId
            ,SName
    from Student 
    where SId in (
        select  distinct 
                SId
        from SC
        where score > 70
    )
) t1 left join SC t2 
on t1.SId = t2.SId
left join Course t3
on t2.CId = t3.CId
order by SId;

35. Check for failed courses

select  distinct
        CId
from SC
where score < 60;

36. The course number is 01 And the course results are in 80 More than 10 points ⽣ Your student number and name

select  SId
        ,SName
from Student
where SId in (
    select  SId
    from SC
    where CId = '01' and score > 80
);

37. Seek every ⻔ Course learning ⽣⼈ Count

select  CId
        ,count(SId) as cnt
from SC
group by CId;

38. The results are not repeated , Check options 「 Zhang San 」⽼ The learning of the courses taught by teachers ⽣ in , The most ⾼ Science ⽣ Information and achievements

set @i := 0;
set @score_front := 0;
set @score_back := 0;
select  tt1.SId
        ,tt1.score
        ,tt2.SName
from (
    select  t1.SId
            ,t1.score
            ,@score_front := t1.score
            ,if(@score_front = @score_back,@i,@i := @i+1) as rk
            ,@score_back := @score_front
    from (
        select  SId
                ,score
        from SC
        where CId in (
            select  CId
            from Course
            where TId in (
                select  TId
                from Teacher
                where TName = ' Zhang San '
            )
        ) order by score desc
    ) t1
) tt1 join Student tt2
on tt1.SId = tt2.SId and tt1.rk = 1;

39. If there is a repetition of the results , Check options 「 Zhang San 」⽼ The learning of the courses taught by teachers ⽣ in , The most ⾼ Science ⽣ Information and achievements

set @i := 0;
set @score_front := 0;
set @score_back := 0;
select  tt1.SId
        ,tt1.score
        ,tt2.SName
from (
    select  t1.SId
            ,t1.score
            ,@score_front := t1.score
            ,if(@score_front = @score_back,@i,@i := @i+1) as rk
            ,@score_back := @score_front
    from (
        select  SId
                ,score
        from SC
        where CId in (
            select  CId
            from Course
            where TId in (
                select  TId
                from Teacher
                where TName = ' Zhang San '
            )
        ) order by score desc
    ) t1
) tt1 join Student tt2
on tt1.SId = tt2.SId and tt1.rk = 1;

40. Query the students who have the same grades in different courses ⽣ Science ⽣ Number 、 Course number 、 learn ⽣ achievement

select  t2.SId
        ,t1.CId
        ,t2.score
from SC t1 
join (
    select  SId
            ,score
            ,count(CId) as cnt
    from SC
    group by SId,score
    having cnt > 1
) t2 on t1.SId = t2.SId and t1.score = t2.score;

41. Query each ⻔ The top two in the course

--  Rank within the group  TopN

42. Count every ⻔ Course learning ⽣ Elective ⼈ Count （ exceed 5 ⼈ The course Statistics ）

select  CId
        ,count(SId) as cnt
from SC
group by CId
having cnt > 5;

43. retrieval ⾄ Take two less courses ⻔ Course learning ⽣ Student number

select  SId
from SC
group by SId
having count(CId) > 2;

44. I have inquired about all the elective courses ⽣ Information

select  SId
        ,SName
from Student 
where SId in (
    select  SId
    from SC
    group by SId
    having count(CId) = (
        select  count(*)
        from Course
    )
);

45. Inquire about each school ⽣ In the age of , Only by year

select  SId
		,SName
		,year(current_timestamp()) - year(SAge) as age
from Student;

46. According to ⽣⽇ Period to calculate , At present ⽉⽇ < Out ⽣ year ⽉ Of ⽉⽇ Then the age decreases ⼀

select  SId
        ,SName
        ,if(now_date>born_date,age,age-1) as new_age
        ,age
from (
    select  SId
            ,SName
            ,year(current_timestamp()) - year(SAge) as age
            ,date_format(current_timestamp(),"%m%d") as now_date
            ,date_format(SAge,"%m%d") as born_date
    from Student
) t1;

47. Query this week ⽣⽇ Science ⽣

select  SId
        ,SName
        ,SAge
from Student
where week(SAge) = week(current_timestamp());

48. Check next week ⽣⽇ Science ⽣

select  SId
        ,SName
        ,SAge
from Student
where week(SAge) = week(DATE_ADD(current_timestamp(),INTERVAL 7 day));

49. Inquiry Book ⽉ too ⽣⽇ Science ⽣

select  SId
        ,SName
        ,SAge
from Student
where month(SAge) = month(current_timestamp());

50. Under query ⽉ too ⽣⽇ Science ⽣

select  SId
        ,SName
        ,SAge
from Student
where month(SAge) = month(DATE_ADD(current_timestamp(),INTERVAL 1 mon));