SQL面试，让你的面试官无fu,ck可说，第17题难倒一片人

SQL语句
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2022-07-24
阿里巴巴码农这修炼秘籍：SQL语句书写规约
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标签   数据库面试

问题及描述：

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

创建测试数据

create table Student(Sid varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10))
insert into Student values('01' , N'化怀彬' , '1990-01-01' , N'男')
insert into Student values('02' , N'肖易' , '1990-12-21' , N'男')
insert into Student values('03' , N'韦达' , '1990-05-20' , N'男')
insert into Student values('04' , N'姜雪' , '1990-08-06' , N'女')
insert into Student values('05' , N'秦蓉' , '1991-12-01' , N'女')
insert into Student values('06' , N'陈丹红' , '1992-03-01' , N'女')
insert into Student values('07' , N'韦瀚瑜' , '1989-07-01' , N'男')
insert into Student values('08' , N'钟爱军' , '1990-01-20' , N'男')
insert into Student values('09' , N'王小凡' , '1985-02-20' , N'男')
insert into Student values('10' , N'于海洲' , '1989-04-13' , N'男')
insert into Student values('11' , N'姜晓亮' , '1992-11-03' , N'男')
insert into Student values('12' , N'王炳洲' , '1989-04-13' , N'男')
insert into Student values('13' , N'闫卫龙' , '1992-11-03' , N'男')
create table Course(Cid varchar(10),Cname nvarchar(10),Tid varchar(10))
insert into Course values('01' , N'语文' , '02')
insert into Course values('02' , N'数学' , '01')
insert into Course values('03' , N'英语' , '03')
create table Teacher(Tid varchar(10),Tname nvarchar(10))
insert into Teacher values('01' , N'小徐老师')
insert into Teacher values('02' , N'欢欢老师')
insert into Teacher values('03' , N'小姜老师')
create table SC(Sid varchar(10),Cid varchar(10),score decimal(18,2))
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)
insert into SC values('08' , '01' , 92)
insert into SC values('08' , '02' , 90)
insert into SC values('08' , '03' , 89)
insert into SC values('09' , '01' , 28)
insert into SC values('09' , '02' , 19)
insert into SC values('09' , '03' , 32)
insert into SC values('10' , '01' , 82)
insert into SC values('10' , '02' , 76)
insert into SC values('10' , '03' , 89)
insert into SC values('11' , '01' , 98)
insert into SC values('11' , '02' , 83)
insert into SC values('11' , '03' , 99)
insert into SC values('12' , '01' , 82)
insert into SC values('12' , '02' , 80)
insert into SC values('12' , '03' , 83)
insert into SC values('13' , '01' , 80)
insert into SC values('13' , '02' , 83)
insert into SC values('13' , '03' , 82)
go

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 > isnull(c.score,0)

2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数

2.1、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

2.2、查询同时存在"01"课程和"02"课程的情况和不存在"01"课程但存在"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 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 isnull(b.score,0) < c.score

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 , a.Sname 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

4.1、查询在sc表存在成绩的学生信息的SQL语句。

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 , a.Sname having cast(avg(b.score) as decimal(18,2)) < 60 order by a.SID

4.2、查询在sc表中不存在成绩的学生信息的SQL语句。

select a.SID , a.Sname , isnull(cast(avg(b.score) as decimal(18,2)),0) avg_score from Student a left join sc b on a.SID = b.SID group by a.SID , a.Sname having isnull(cast(avg(b.score) as decimal(18,2)),0) < 60 order by a.SID

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,a.Sname 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,a.Sname 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 N'李%'
--方法2
select count(Tname) ["李"姓老师的数量] from Teacher where left(Tname,1) = N'李' /* "李"姓老师的数量 ----------- 1 */

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 = N'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 = N'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2
select Student.* from Student , SC where Student.SID = SC.SID and SC.CID = '02' and exists (Select 1 from SC SC_2 where SC_2.SID = SC.SID and SC_2.CID = '01') order by Student.SID
--方法3
select m.* from Student m where SID in ( select SID from ( select distinct SID from SC where CID = '01' union all select 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

11.1、

select Student.* from Student , SC where Student.SID = SC.SID group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(CID) < (select count(CID) from Course)

11.2

select Student.* from Student left join SC on Student.SID = SC.SID group by Student.SID , Student.Sname , Student.Sage , Student.Ssex having count(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 Student.* from Student where SID in (select distinct SC.SID from SC where SID <> '01' and SC.CID in (select distinct CID from SC where SID = '01') group by SC.SID having count(1) = (select count(1) from SC where SID='01'))

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 = N'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 静态

select a.SID 学生编号 , a.Sname 学生姓名 , max(case c.Cname when N'语文' then b.score else null end) [语文], max(case c.Cname when N'数学' then b.score else null end) [数学], max(case c.Cname when N'英语' then b.score else null end) [英语], cast(avg(b.score) 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

17.2 动态

declare @sql nvarchar(4000) set @sql = 'select a.SID ' + N'学生编号' + ' , a.Sname ' + N'学生姓名' select @sql = @sql + ',max(case c.Cname when N'''+Cname+''' then b.score else null end) ['+Cname+']' from (select distinct Cname from Course) as t set @sql = @sql + ' , cast(avg(b.score) as decimal(18,2)) ' + N'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 ' + N'平均分' + ' desc' exec(@sql)
阿里巴巴码农这修炼秘籍：SQL语句书写规约
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