MySQL经典50题_网站优化分享_上海毫米网络优化公司

一、数据表介绍

1.学生表 Student(SId,Sname,Sage,Ssex) --SId 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别

2.课程表 Course(CId,Cname,TId) --CId 课程编号,Cname 课程名称,TId 教师编号

3.教师表 Teacher(TId,Tname) --TId 教师编号,Tname 教师姓名

4.成绩表 SC(SId,CId,score) --SId 学生编号,CId 课程编号,score 分数

学生表 Student
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' , '1990-12-20' , '男');
insert into Student values('04' , '李云' , '1990-12-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-01-01' , '女');
insert into Student values('07' , '郑竹' , '1989-01-01' , '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' , '2012-06-06' , '女');
insert into Student values('12' , '赵六' , '2013-06-13' , '女');
insert into Student values('13' , '孙七' , '2014-06-01' , '女');
科目表 Course
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');
教师表 Teacher
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');
成绩表 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);

二、练习题

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 s.*, sc1.score, sc2.score
from student s
join SC sc1
on s.SId = sc1.SId
join SC sc2
on sc1.SId = sc2.CId and sc1.CId = "01" and sc2.CId = "02"
where sc1.score > sc2.score;

2. 查询同时存在" 01 "课程和" 02 "课程的情况

select s1.SId, s1.score,s2.score
from  (select SId, score from SC where CId ="01") s1, 
(select SId, score from SC where CId ="02") s2 
where s1.SId = s2.SId;

3. 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 SC a
left join SC b
on a.SId = b.SId and b.CId = "02"
where a.CId = "01";

4. 查询不存在" 01 "课程但存在" 02 "课程的情况

select *
from (select * from SC s where s.CId = "02") as a
where a.SId not in (select SId from SC s where s.CId = "01");

5. 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 SC.SId, s.Sname, AVG(score)
from student s, SC
where s.SId = SC.SId
group by SC.SId
having AVG(score) >= 60;

6. 查询在 SC 表存在成绩的学生信息

select * 
from student
where student.SId in (select SId from SC);

7. 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 s.SId, s.Sname, b.cnt, b.sum_s
from student s
left join (select SId, count(CId) as cnt, sum(score) as sum_s
          	from SC group by SId) as b
on s.SId = b.SId;

8. 查有成绩的学生信息

select *
from student
where SId in (select SId from SC group by SId);

9. 查询「李」姓老师的数量

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

10. 查询学过「张三」老师授课的同学的信息

select s.*, Tname
from student s
inner join(
	select SC.*, Tname
	from SC
	inner join(
 	   select course.*, Tname
	   from course
	   inner join teacher as th
	   on course.TId = th.TId) as a
	on SC.CId = a.CId) as b
on s.SId = b.SId
where Tname = '张三';

11. 查询没有学全所有课程的同学的信息

select s.*
from student s
inner join(
	select SId, count(CId) as cnt
	from SC
	group by SId
	having cnt < (select count(CId) from course)) as a
on s.SId = a.SId;

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

select distinct s.*
from student s
inner join (
	select *
	from SC
	where CId in(
   	    select CId
		from SC
		where SId = "01")) as b
on s.SId = b.SId;

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 s.*
from student s
inner join (
	select SId
	from SC
	where SId not in (
		select SId
		from SC
		where CId not in (
			select CId
  		    from SC
   		    where SId = "01")) and SId != "01"
	group by SId
	having count(CId) = (select count(CId) from SC where SId = "01")) as a
on s.SId = a.SId;

14. 查询没学过"张三"老师讲授的任一门课程的学生姓名

select Sname
from student s
where SId not in (
	select SId
	from SC
	left join course cou
	on SC.CId = cou.CId
	inner join teacher th
	on cou.TId = th.TId
	where Tname = "张三");

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 b.SId, s.Sname, avg_sc
from (
    select SC.SId, AVG(score) as avg_sc
	from SC
	inner join(
		select SId
   	    from SC
    	where score < 60
  	    group by SId
   	    having count(CId) >= 2) as a
	on SC.SId = a.SId
	group by SC.SId) as b
left join student s
on b.SId = s.SId;

16. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息

select s.*, a.score
from student s
right join(
	select SId, score
	from SC
	where CId = "01" and score <60) as a
on s.SId = a.SId
order by a.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 a.SId, a.CId, a.Score, avg_sc
from (
	select s.SId, SC.CId, SC.Score
	from student s
	left join SC
	on s.SId = SC.SId) as a
left join (
	select SId, AVG(score) as avg_sc
	from SC
	group by SId) as b
on a.SId = b.SId
order by b.avg_sc 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
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 a.*, b.Cname
from(
	select CId,
    count(*) as 选修人数,
    max(score) as 最高分,
    min(score) as 最低分,
    avg(score) as 平均分,
    sum(case when score >= 60 then 1 else 0 end) / count(*) as 及格率,
    sum(case when score >= 70 and score < 80 then 1 else 0 end) / count(*) as 中等率,
    sum(case when score >= 80 and score < 90 then 1 else 0 end) / count(*) as 优良率,
    sum(case when score >= 90 then 1 else 0 end) / count(*) as 优秀率
    from SC
    group by CId
    order by count(*) desc, CId asc) as a
left join course as b
on a.CId = b.CId;

19. 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 *, row_number() 
over (partition by CId order by score desc) as 排名
from SC;

20. 按各科成绩进行排序，并显示排名， Score 重复时合并名次

select *, rank()
over (partition by CId order by score desc) as 排名
from SC;

21. 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 *, rank()
over (order by sum_s desc) as 排名
from (select SId, sum(score) as sum_s
     from SC
     group by SId) as a;

22. 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 *,dense_rank()
over (order by sum_sc desc) as 排名
from(select SId, sum(score) as sum_sc
    from SC
    group by SId) as a;

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]，[60-0] 及所占百分比

select b.*, a.Cname
from course as a
right join(
	select CId,
	concat(sum(case when score > 0 and score < 60 then 1 else 0 end) / count(*) * 100, '%') as '[0-60]',
	concat(sum(case when score >= 60 and score < 70 then 1 else 0 end) / count(*) * 100, '%') as '[60-70]',
	concat(sum(case when score >= 70 and score < 85 then 1 else 0 end) / count(*) * 100, '%') as '[70-85]',
	concat(sum(case when score >= 85 and score <= 100 then 1 else 0 end) / count(*) * 100, '%') as '[85-100]'
	from SC
	group by CId) as b
on a.CId = b.CId;

24. 查询各科成绩前三名的记录

select *
from(
    select *,dense_rank()
	over (partition by CId order by score desc) as rnk
	from SC) as a
where rnk <= 3;

25. 查询每门课程被选修的学生数

select CId, count(*) as 学生数
from SC
group by CId;

26. 查询出只选修两门课程的学生学号和姓名

select a.SId, s.Sname
from student s
right join(
	select SId, count(*) as 课程数
	from SC
	group by SId
	having 课程数 = 2) as a
on s.SId = a.SId;

27. 查询男生、女生人数

select Ssex, count(*) as num
from student
group by Ssex;

28. 查询名字中含有「风」字的学生信息

select *
from student
where Sname like "%风%";

29. 查询同名同性学生名单，并统计同名人数

select Sname, Ssex, count(*) as 同名人数
from (
	select s.*
	from student s
	inner join student a
	on s.Sname = a.Sname and s.Ssex = a.Ssex and s.SId != a.SId) as a
group by Sname, Ssex;

30. 查询 1990 年出生的学生名单

select *
from student
where year(Sage) = "1990";

31. 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 CId, avg(score) as avg_sc
from SC
group by CId
order by avg_sc desc, CId asc;

32. 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.SId, s.Sname, avg_sc
from student s
right join(
	select SId, avg(score) as avg_sc
	from SC
	group by SId
	having avg_sc >= 85) as a
on s.SId = a.SId;

33. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

select s.SId, s.Sname, SC.CId, SC.score
from SC
left join student s
on SC.SId = s.SId
where CId = (
	select CId
	from course
	where Cname = "数学") and score < 60;

34. 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 *
from student s
left join SC
on s.SId = SC.SId;

35. 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 s.Sname, c.Cname, SC.score
from SC
left join course as c
on SC.CId = c.CId
left join student s
on SC.SId = s.SId
where SC.score > 70;

36. 查询不及格的课程

select *
from course
where CId in (
    select distinct CId
    from SC
    where score < 60);

37. 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 s.SId, s.Sname
from student s
join SC
on s.SId = SC.SId
where SC.CId = "01" and SC.score > 80;

38. 求每门课程的学生人数

select CId, count(*)
from SC
group by CId;

39. 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 s.*, SC.score
from student s, teacher th, course c, SC
where th.TId = c.TId
and SC.SId = s.SId
and SC.CId = c.CId
and th.Tname = "张三"
order by score desc
limit 1;

40. 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 s.*, SC.score
from student s
join SC
on s.SId = SC.SId
join course c
on SC.CId = c.cId
join teacher th
on c.TId = th.TId
where th.Tname = "张三"
order by score desc
limit 0,1;

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 s.SId, s.Sname, a.CId, a.score, b.CId, b.score
from student s
join SC a
on a.SId = s.SId
join SC b 
on b.SId = s.SId
where a.CId != b.CId and a.score = b.score;

42. 查询每门功成绩最好的前两名

select s.*, a.*
from student s
left join (
    select SC.SId, SC.score, row_number()
    over (partition by SC.CId) ranks
    from SC) as a
on s.SId = a.SId
where a.ranks <= 2;

43. 统计每门课程的学生选修人数（超过 5 人的课程才统计）。

select SC.CId, count(*)
from SC
join course c
on SC.CId = c.CId
group by SC.CId
having count(*) > 5;

44. 检索至少选修两门课程的学生学号

select s.SId
from SC
join student s
on SC.SId = s.SId
group by SC.SId
having count(*) >= 2;

45. 查询选修了全部课程的学生信息

select s.*
from SC
join student s
on SC.SId = s.SId
group by SC.SId
having count(*) = (select count(*) from course);

46. 查询各学生的年龄，只按年份来算

select s.*, year(now()) - year(s.Sage) 年龄
from student s;

47. 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.*, timestampdiff(year, s.Sage, curdate()) 年龄
from student s;

48. 查询本周过生日的学生

select s.*
from student s
where weekofyear(s.Sage) = weekofyear(now());

49. 查询下周过生日的学生

select s.*
from student s
where weekofyear(s.Sage) = weekofyear(now()) + 1;

50. 查询本月过生日的学生

select s.*
from student s
where month(s.Sage) = month(now());

51. 查询下月过生日的学生

select s.*
from student s
where month(s.Sage) = month(now()) + 1;

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