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数据库面试题+解析

2022-07-07 21:52:00 天蝎座的程序员

以下是四张表,1.学生表-t_student,2.教师表-t_teacher,3.课程表-t_course, 4.成绩表-t_score

下面是表设计:

-- 1.学生表-t_student
-- sid 学生编号,sname 学生姓名,sage 学生年龄,ssex 学生性别
create table t_student(
	sid varchar(10) primary key comment '学生编号',
	sname varchar(20) not null comment '学生姓名',
	sage varchar(10) not null comment '学生年龄',
	sex varchar(20) not null comment '学生性别'
)comment '学生信息表';

-- 2.教师表-t_teacher
-- tid 教师编号,tname 教师名称
create table t_teacher(
	tid varchar(10) primary key comment '教师编号',
	tname varchar(20) not null comment '教师名称'
)comment '教师信息表';

-- 3.课程表-t_course
-- cid 课程编号,cname 课程名称,tid 教师名称
create table t_course(
	cid varchar(10) primary key comment '课程编号',
	cname varchar(20) not null comment '课程名称',
	tid varchar(10) not null comment '教师名称',
	foreign key(tid) references t_teacher(tid)
)comment '课程信息表';

-- 4.成绩表-t_score
-- sid 学生编号,cid 课程编号,score 成绩
create table t_score(
	sid varchar(10) not null comment '学生编号',
	cid varchar(10) not null comment '课程编号',
	score float default 0 comment '成绩',
	foreign key(sid) references t_student(sid),
	foreign key(cid) references t_course(cid)
)comment '成绩信息表';

select * from t_student;
select * from t_teacher;
select * from t_course;
select * from t_score;

下面是面试题+解题结果(解题的方式不是只有这一种,我写的而只是其中之一)

#01)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.*,temp.s1,temp.s2 from(
select t1.sid,t1.s1,t2.s2 from
(select sid,score as s1 from t_score where cid='01')t1,
(select sid,score as s2 from t_score where cid='02')t2
where t1.sid=t2.sid and t1.s1>t2.s2)temp,t_student s
where temp.sid=s.sid

#02)查询同时存在" 01 "课程和" 02 "课程的情况

select* from
(select sid,score as s1 from t_score where cid='01') t1,
(select sid,score as s2 from t_score where cid='02') t2
where t1.sid=t2.sid;

#03)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 sid,score from t_score where cid='01')t1 left join
(select sid,score from t_score where cid='02')t2 on t1.sid=t2.sid

#04)查询不存在" 01 "课程但存在" 02 "课程的情况

select * from t_score where sid not in (
select sid from t_score where cid='01') and cid='02';

select * from t_score where sid='07';

#05)查询平均成绩(分组 group by,筛选:having avg)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 s.sid,s.sname,
round(avg(sc.score),2) score
from
t_student s,t_score sc
where s.sid=sc.sid
group by s.sid,s.sname
having avg(sc.score)>=60;

#06)查询在t_score表存在成绩的学生信息

select distinct s.*
from
t_score sc,t_student s where sc.sid=s.sid

#07)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, count(sc.cid) cn,
sum(sc.cid) sm
from 
t_student s left join t_score sc on sc.sid=s.sid
group by s.sid,s.sname

#08)查询「李」姓老师的数量

select count(tid) from t_teacher where tname like '李%';

#09)查询学过「张三」老师授课的同学的信息

select
s.*
from t_teacher t,
t_course c,
t_score sc,
t_student s
where 
t.tid=c.tid and
c.cid=sc.cid and
sc.sid=s.sid and t.tname='张三'

#10)查询没有学全所有课程的同学的信息

select * from t_student where sid not in (
select sid from t_score 
group by sid having count(cid)=(select count(cid) from t_course))

#11)查询没学过"张三"老师讲授的任一门课程的学生姓名

select * from t_student where sid not in(
select sc.sid from t_teacher t,t_course c,t_score sc where
t.tid=c.tid and t.tname='张三' and
c.cid=sc.cid)

#12)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
s.sid,
s.sname,
round(avg(sc.score),2) sc
from t_score sc,t_student s
where sc.sid=s.sid and sc.score<60
group by s.sid,s.sname
having count(sc.cid)>1

#13)检索" 01 "课程分数小于 60,按分数降序排列的学生信息

select *
from t_student a,
    t_score b
where a.sid = b.sid
  and b.cid = '01'
  and score < 60
order by score desc;

#14)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.sid,
round(avg(sc.score),2) as '平均成绩',
sum(if(sc.cid='01',sc.score,0)) as '语文',
sum(if(sc.cid='02',sc.score,0)) as '数学',
sum(if(sc.cid='03',sc.score,0)) as '英语'
from
t_score sc
group by sc.sid,sc.cid
order by avg(sc.score) desc

#15)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 
c.cid,
 c.cname,
 count(c.cid) as '选修人数',
 max(sc.score) as '最高分',                                         
 min(sc.score) as '最低分',
round(avg(sc.score),2) as '平均分',
 concat(round(sum(if(sc.score>=60,1,0))/count(s.sid)*100,2),'%') as '及格率',
 concat(round(sum(if(sc.score>=70 and sc.score<80,1,0))/count(s.sid)*100,2),'%') as '中等率',
 concat(round(sum(if(sc.score>=80 and sc.score<90,1,0))/count(s.sid)*100,2),'%') as '优良率',
concat(round(sum(if(sc.score>=90,1,0))/count(s.sid)*100,2),'%') as '优秀率'
from
t_score sc,t_course c,t_student s
where
sc.cid=c.cid and sc.sid=s.sid
group by c.cid,c.cname

以上就是今天的分享,在面试官给你题目的时候,你面前是没与电脑的,你需要在脑海中构思你的表设计。这是面试的一大难题,需要足够的空间想象能力。good luck!

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本文为[天蝎座的程序员]所创,转载请带上原文链接,感谢
https://blog.csdn.net/m0_62246061/article/details/125612329