Mysql经典面试题及答案

需要数据库表
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

添加测试数据
1.学生表

create table Student(SID varchar(10),Sname nvarchar(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');

2.课程表

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');

3.教师表

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

4.成绩表

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);

–1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数–
----1.1、查询同时存在"01"课程和"02"课程的情况

select a.* , b.score 课程01的分数,c.score 课程02的分数
from Student a , SC b , SC c
where a.SID = b.SID and a.SID = c.SID and b.CID = '01' and c.CID = '02' and b.score > c.score

----1.2、查询同时存在"01"课程和"02"课程的情况和存在"01"课程但可能不存在"02"课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)

select a.* , b.score 课程01的分数,c.score 课程02的分数 from Student a
left join SC b on a.SID = b.SID and b.CID = '01'
left join SC c on a.SID = c.SID and c.CID = '02'
where b.score is not null

–3、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 a.SID , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_score
from Student a , sc b
where a.SID = b.SID
group by a.SID
having cast(avg(b.score) as decimal(18,2)) >= 60
order by a.SID

–4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩–4.2、查询在sc表中不存在成绩的学生信息的SQL语句。
运行时间 1>2>3,推荐使用第三种方法
法一

SELECT s.*
from student s
where s.SID NOT IN(select SID from sc)

法二

SELECT s.*
from student s
LEFT JOIN sc a ON s.SID = a.SID
WHERE a.SID is NULL

法三

SELECT s.*
from student s
WHERE
(SELECT COUNT(1) FROM sc a WHERE s.SID = a.SID) = 0

–5、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
----5.1、查询所有有成绩的SQL。

select a.SID 学生编号 , a.Sname 学生姓名 , count(b.CID) 选课总数, sum(score) 所有课程的总成绩
from Student a , SC b
where a.SID = b.SID
group by a.SID
order by a.SID

----5.2、查询所有(包括有成绩和无成绩)的SQL。

select a.SID 学生编号 , a.Sname 学生姓名 , count(b.CID) 选课总数, sum(score) 所有课程的总成绩
from Student a left join SC b
on a.SID = b.SID
group by a.SID
order by a.SID

–6、查询"李"姓老师的数量

--方法1
select count(Tname) 李姓老师的数量 from Teacher where Tname like '李%'--方法2
select count(Tname) 李姓老师的数量 from Teacher where left(Tname,1) = '李'

–7、查询学过"张三"老师授课的同学的信息

select distinct Student.*
from Student , SC , Course , Teacher
where Student.SID = SC.SID and SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '张三'
order by Student.SID

–8、查询没学过"张三"老师授课的同学的信息

select m.*
from Student m
where SID not in (select distinct SC.SID from SC , Course , Teacher where SC.CID = Course.CID and Course.TID = Teacher.TID and Teacher.Tname = '张三')
order by m.SID

–9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息

--方法1
select Student.*
from Student , SC
where Student.SID = SC.SID and SC.CID = '01' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02')
order by Student.SID--方法2select m.*
from Student m
where SID in(select SID from(select distinct SID from SC where CID = '01'union allselect distinct SID from SC where CID = '02') t group by SID having count(1) = 2
)
order by m.SID

–10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息

--方法1
select Student.*
from Student , SC
where Student.SID = SC.SID and SC.CID = '01' and not exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02')
order by Student.SID--方法2
select Student.*
from Student , SC
where Student.SID = SC.SID and SC.CID = '01' and Student.SID not in (Select SC_2.SID from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '02')
order by Student.SID

–11、查询没有学全所有课程的同学的信息

SELECT s.*,COUNT(a.CID)
FROM student s
LEFT JOIN sc a ON s.SID = a.SID
GROUP BY s.SID
HAVING COUNT(a.CID)<(SELECT COUNT(CID) FROM course)

–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息

select distinct Student.*
from Student , SC
where Student.SID = SC.SID and SC.CID in (select CID from SC where SID = '01') and Student.SID <> '01'

–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 tt.SID FROM(SELECT s.SID ,GROUP_CONCAT(s.CID separator ',') AS ccFROM(SELECT *  FROM sc ORDER BY SID,CID ) s GROUP BY s.SID) tt
WHERE tt.cc =(SELECT GROUP_CONCAT(a.CID separator ',') FROM (SELECT *  FROM sc WHERE SID='01' ORDER BY SID,CID) a )

–14、查询没学过"张三"老师讲授的任一门课程的学生姓名

select student.*
from student
where student.SID not in(select distinct sc.SID from sc , course , teacher where sc.CID = course.CID and course.TID = teacher.TID and teacher.tname = '张三')
order by student.SID

–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 student.SID , student.sname , cast(avg(score) as decimal(18,2)) avg_score from student , sc
where student.SID = SC.SID and student.SID in (select SID from SC where score < 60 group by SID having count(1) >= 2)
group by student.SID , student.sname

–16、检索"01"课程分数小于60，按分数降序排列的学生信息

select student.* , sc.CID , sc.score from student , sc
where student.SID = SC.SID and sc.score < 60 and sc.CID = '01'
order by sc.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–17.1 SQL 2000 静态

select a.SID 学生编号 , a.Sname 学生姓名 ,
max(case c.Cname when '语文' then b.score else null end) 语文 ,
max(case c.Cname when '数学' then b.score else null end) 数学 ,
max(case c.Cname when '英语' then b.score else null end) 英语 ,
cast(SUM(b.score)/(SELECT COUNT(1) FROM course) as decimal(18,2)) 平均分
from Student a
left join SC b on a.SID = b.SID
left join Course c on b.CID = c.CID
group by a.SID , a.Sname
order by 平均分 desc

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