SQL笔试 I 经典44题及答案解析

01 建表语句

create table Student(sid varchar(10),sname varchar(10),sage datetime,ssex nvarchar(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('08' , '王菊' , '1990-01-20' , '女');
create table Course(cid varchar(10),cname varchar(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');
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');
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);

02 表结构预览

#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

#课程表
Course(CId,Cname,TId)
CId 课程编号,Cname 课程名称,TId 教师编号

#教师表
Teacher(TId,Tname)
TId 教师编号,Tname 教师姓名

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

1. 查询“01”课程比“02”课程成绩高的所有学生的学号；

select distinct t1.sid as sid from (select * from sc where cid='01') t1 left join (select * from sc where cid='02') t2 on t1.sid=t2.sid where t1.score > t2.score

2. 查询平均成绩大于60分的同学的学号和平均成绩；

select sid, avg(score) from sc group by sid having avg(score)>60

3. 查询所有同学的学号、姓名、选课数、总成绩

select student.sid as sid,sname,count(distinct cid) course_cnt,sum(score) as total_score from student left join sc on student.sid=sc.sid group by sid,sname

4. 查询姓“李”的老师的个数；

select count(distinct tid) as teacher_cnt from teacher where tname like '李%'

5. 查询没学过“张三”老师课的同学的学号、姓名；

select sid,sname from student where sid not in (select sc.sid from teacher left join course on teacher.tid=course.tid left join sc on course.cid=sc.cid where teacher.tname='张三')

6. 查询学过“01”并且也学过编号“02”课程的同学的学号、姓名；

select t.sid as sid,sname from (select sid,count(if(cid='01',score,null)) as count1,count(if(cid='02',score,null)) as count2 from sc group by sid having count(if(cid='01',score,null))>0 and count(if(cid='02',score,null))>0)t left join student on t.sid=student.sid

7. 查询学过“张三”老师所教的课的同学的学号、姓名；

select student.sid,sname from (select distinct cid from course left join teacher on course.tid=teacher.tid where teacher.tname='张三')course left join sc on course.cid=sc.cid left join student on sc.sid=student.sid group by student.sid,sname

8. 查询课程编号“01”的成绩比课程编号“02”课程低的所有同学的学号、姓名；

select t1.sid,sname from (select distinct t1.sid as sid from (select * from sc where cid='01')t1 left join (select * from sc where cid='02')t2 on t1.sid=t2.sid where t1.score>t2.score)t1 left join student on t1.sid=student.sid

9. 查询所有课程成绩小于60分的同学的学号、姓名；

select t1.sid,sname from (select sid,max(score) from sc group by sid having max(score<60))t1 left join student on t1.sid=student.sid

10. 查询没有学全所有课的同学的学号、姓名；

select t1.sid,sname from (select count(cid),sid from sc group by sid having count(cid) < (select count(distinct cid) from course))t1 left join student on t1.sid=student.sid

11. 查询至少有一门课与学号为“01”的同学所学相同的同学的学号和姓名；

#思路：1.找出学号为“01”的同学所学的课程，2.找出有相同课程的同学

#select sid from demo.sc
#left join
#(select cid from demo.sc where sid="01") t
#on t.cid=sc.cid;

select t2.sid,sname from demo.student
left join
(select distinct sc.sid as sid from  ( select cid from demo.sc where sid='01' )t1 left join demo.sc on t1.cid=sc.cid) t2
on t2.sid=student.sid
having t2.sid

12. 查询和"01"号的同学学习的课程完全相同的其他同学的学号和姓名

#注意是和'01'号同学课程完全相同但非学习课程数相同的,这里我用左连接解决这个问题
select t1.sid,sname from 
( select sc.sid ,count(distinct sc.cid) from 
( select cid from sc where sid='01' )t1#选出01的同学所学的课程 
left join sc on t1.cid=sc.cid group by sc.sid 
having count(distinct sc.cid)= (select count(distinct cid) from sc where sid = '01')    )t1
left join student on t1.sid=student.sid
where t1.sid!='01'

13. 把“SC”表中“张三”老师教的课的成绩都更改为此课程的平均成绩；

暂跳过update题目

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
where sid not in
(
select distinct sid from sc
left join course on sc.cid=course.cid
left join teacher on course.tid=teacher.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

#方式一
select t.sid as sid,sname, t.score as score
from student
left join
(select sid,cid,score from sc
where cid="01" and score<60
order by score) t
on t.sid=student.sid
where t.sid is not null;

#方式二
select t1.sid,sname,avg_score from
(select sid,count(if(score<60,cid,null)),avg(score) as avg_score from sc group by sid having count(if(score<60,cid,null)) >=2 )t1
left join student
on t1.sid=student.sid

16. 检索"01"课程分数小于60，按分数降序排列的学生信息

#方式一
select t.sid as sid,sname,t.avg_score as avg_score
from student left join
(select sid,avg(score) as avg_score from sc group by sid) t
on t.sid=student.sid
where t.sid is not null
order by avg_score desc;

#方式二
select sid,if(cid='01',score,100)from sc
where if(cid='01',score,100)<60
order by if(cid='01',score,100) desc

17. 按平均成绩从高到低显示所有学生的平均成绩

#方式一
select t.sid as sid,sname,t.avg_score as avg_score
from student
left join
(select sid,avg(score) as avg_score
from sc
group by sid) t
on t.sid=student.sid
where t.sid is not null
order by avg_score desc;

#方式二
select sid,avg(score)from sc
group by sid
order by avg(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

#方式一
select t.cid,cname,t.max_score,t.min_score,t.avg_score,t.pass_rate
from course
left join
(select cid,max(score) as max_score,min(score) as min_score,avg(score) as avg_score,count(if(score>=60,sid,null))/count(sid) as pass_rate
from sc
group by cid) t
on t.cid=course.cid;

#方式二
select sc.cid ,cname ,max(score) as max_score ,min(score) as min_score ,avg(score) as avg_score ,count(if(score>=60,sid,null))/count(sid) as pass_rate 
from sc  left join course 
on sc.cid=course.cid 
group by sc.cid

19. 按各科平均成绩从低到高和及格率的百分数从高到低顺序

#这里先按照平均成绩排序，再按照及格百分数排序，
select cid ,avg(score) as avg_score ,count(if(score>=60,sid,null))/count(sid) as pass_rate
from sc
group by cid
order by avg_score,pass_rate desc

20. 查询学生的总成绩并进行排名

select sid ,sum(score) as sum_score
from sc
group by sid
order by sum_score desc

21. 查询不同老师所教不同课程平均分从高到低显示

select tid, avg(score) as avg_score
from course
left join sc
on course.cid=sc.cid
group by tid
order by avg_score 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 sid,rank_num,score,cid
from ( select rank() over(partition by cid order by score desc) as rank_num ,sid ,score ,cid from sc )t
where rank_num in (2,3)

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 sc.cid ,cname ,
count(if(score between 85 and 100,sid,null))/count(sid) ,
count(if(score between 70 and 85,sid,null))/count(sid) ,
count(if(score between 60 and 70,sid,null))/count(sid) ,
count(if(score between 0 and 60,sid,null))/count(sid)
from sc
left join course 
on sc.cid=course.cid
group by sc.cid,cname

24. 查询学生平均成绩及其名次

select sid ,avg_score ,rank() over (order by avg_score desc)
from  ( select sid ,avg(score) as avg_score from sc group by sid )t

25. 查询各科成绩前三名的记录

select sid,cid,rank1
from 
( 
select cid ,sid ,rank() over(partition by cid order by score desc) as rank1 
from sc 
)t
where rank1<=3

26. 查询每门课程被选修的学生数

select count(sid) ,cid
from sc
group by cid

27. 查询出只选修了一门课程的全部学生的学号和姓名

select sid
from sc
group by sid
having count(cid) =1

28. 查询男生、女生人数

select ssex ,count(distinct sid)
from student
group by ssex

29. 查询名字中含有"风"字的学生信息

select sid,sname
from student
where sname like '%风%'

30. 查询同名同性学生名单，并统计同名人数

select ssex ,sname ,count(sid)
from student
group by ssex,sname
having count(sid)>=2

31. 查询1990年出生的学生名单(注：Student表中Sage列的类型是datetime)

select sid,sname,sage
from student
where year(sage)=1990

32. 查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列

select cid,avg(score) as avg_score
from sc
group by cid
order by avg_score,cid desc

33. 查询不及格的课程，并按课程号从大到小排列

select cid,sid,score
from sc
where score<60
order by cid desc,sid

34. 查询课程编号为"01"且课程成绩在60分以上的学生的学号和姓名；

select sid,cid,score
from sc
where cid='01' and score>60

35. 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

select sc.sid,sname,cname,score
from sc
left join course style="font-weight: 600;">=course.cid
left join teacher style="font-weight: 600;">=teacher.tid
left join student style="font-weight: 600;">=student.sid
where tname='张三'
order by score desc
limit 1;

36. 查询每门功课成绩最好的前两名

select cid,sid,rank1
from 
(
select cid,sid,rank() over(partition by cid order by score desc) as rank1
from sc
)t
where rank1 <=2

37. 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 cid,count(sid) as cnt
from sc
group by cid
having cnt>=5
order by count(sid) desc,cid

38. 检索至少选修两门课程的学生学号

select sid,count(cid)
from sc
group by sid
having count(cid)>=2

39. 查询选修了全部课程的学生信息

select sid,count(cid)
from sc
group by sid
having count(cid)=(select count(distinct cid) from sc)

40. 查询各学生的年龄

select
sid,sname,year(curdate())-year(sage) as sage
from student

41.查询本周过生日的学生

select sid,sname,sage
from student
where weekofyear(sage)=weekofyear(curdate())

42.查询下周过生日的学生

select sid,sname,sage
from student
where weekofyear(sage) = weekofyear(date_add(curdate(),interval 1 week))

43.查询本月过生日的学生

select sid,sname,sage
from student
where month(sage) = month(curdate())

44. 查询下月过生日的学生

select sid,sname,sage
from student
where month(date_sub(sage,interval 1 month)) = month(curdate())