写了这么多JAVA基础，来点SQL吧！

一般面试时考SQL，主要就是考你“统计分析”这一块，下面我们来看面试官经常采用的手段。

由4张简单的不能再简单的表，演变出50道SQL

哈哈哈哈，够这个面试官面个15，20个人，不带重复的了，而且每个SQL你真的不动动脑子还写不出呢，你别不服气，下面开始。

表结构：

表Student

(S#,Sname,Sage,Ssex) 学生表

S#	student_no
Sage	student_age
Ssex	student_sex

表Course

(C#,Cname,T#) 课程表

C#	course_no
Cname	course_name
T#	teacher_no

表SC（学生与课程的分数mapping 表）

(S#,C#,score) 成绩表

S#	student_no
C#	course_no
score	分数啦

表Teacher

(T#,Tname) 教师表

T#	teacher_no
Tname	teacher_name

50道问题开始

1、查询“001”课程比“002”课程成绩高的所有学生的学号；

  select a.S# from (select s#,score from SC where C#='001') a,(select s#,score

  from SC where C#='002') 

  where a.score>b.score and a.s#=b.s#;

2、查询平均成绩大于60分的同学的学号和平均成绩；

    select S#,avg(score)

    from sc

    group by S# having avg(score) >60;

3、查询所有同学的学号、姓名、选课数、总成绩；

  select Student.S#,Student.Sname,count(SC.C#),sum(score)

  from Student left Outer join SC on Student.S#=SC.S#

  group by Student.S#,Sname

4、查询姓“李”的老师的个数；

  select count(distinct(Tname))

  from Teacher

  where Tname like '李%';

5、查询没学过“叶平”老师课的同学的学号、姓名；

    select Student.S#,Student.Sname

    from Student 

    where S# not in (select distinct( SC.S#) fromSC,Course,Teacher where  SC.C#=Course.C#and Teacher.T#=Course.T# andTeacher.Tname='叶平');

6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；

  select Student.S#,Student.Sname fromStudent,SC where Student.S#=SC.S# andSC.C#='001'and exists( Select * from SC as SC_2 where SC_2.S#=SC.S# and SC_2.C#='002');

7、查询学过“叶平”老师所教的所有课的同学的学号、姓名；

  select S#,Sname

  from Student

  where S# in (select S# from SC,Course ,Teacher where SC.C#=Course.C# andTeacher.T#=Course.T# and Teacher.Tname='叶平'group by S# having count(SC.C#)=(select count(C#) fromCourse,Teacher  whereTeacher.T#=Course.T# and Tname='叶平'));

8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；

  Select S#,Sname from (select Student.S#,Student.Sname,score ,(select score from SC SC_2 where SC_2.S#=Student.S#and SC_2.C#='002') score2

  from Student,SC where Student.S#=SC.S# andC#='001') S_2 where score2 <score;

9、查询所有课程成绩小于60分的同学的学号、姓名；

  select S#,Sname

  from Student

  where S# not in (select Student.S# fromStudent,SC where S.S#=SC.S# andscore>60);

10、查询没有学全所有课的同学的学号、姓名；

    select Student.S#,Student.Sname

    from Student,SC

    whereStudent.S# =SC.S# group by  Student.S#,Student.Sname having count(C#) <( select count(C#) from Course); 

11、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名；

    select S#,Sname from Student,SC whereStudent.S#=SC.S# and C# in select C# from SC where S#='1001';

12、查询至少学过学号为“001”同学所有一门课的其他同学学号和姓名；

    select distinct SC.S#,Sname

    from Student,SC

    where Student.S#=SC.S# and C# in(select C# from SC where S#='001');

13、把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩；

    update SC set score=(select avg(SC_2.score)

    from SC SC_2

    where SC_2.C#=SC.C# ) fromCourse,Teacher where Course.C#=SC.C# andCourse.T#=Teacher.T# and Teacher.Tname='叶平');

14、查询和“1002”号的同学学习的课程完全相同的其他同学学号和姓名；

    select S# from SC where C# in(select C# from SC where S#='1002')

    group by S# having count(*)=(select count(*) from SC where S#='1002');

15、删除学习“叶平”老师课的SC表记录；

    DelectSC

    from course ,Teacher 

    where Course.C#=SC.C# and Course.T#=Teacher.T# and Tname='叶平';

16、向SC表中插入一些记录，这些记录要求符合以下条件：没有上过编号“003”课程的同学学

号、2号课的平均成绩；

    Insert SC select S#,'002',(Select avg(score)

    from SC where C#='002') from Student where S# notin (Select S# from SC where C#='002');

17、按平均成绩从高到低显示所有学生的“数据库”、“企业管理”、“英语”三门的课程成绩，按

如下形式显示： 学生ID,,数据库,企业管理,英语,有效课程数,有效平均分

    SELECT S# as 学生ID

        ,(SELECT score FROM SC WHERE SC.S#=t.S#AND C#='004') AS 数据库

        ,(SELECT score FROM SC WHERE SC.S#=t.S#AND C#='001') AS 企业管理

        ,(SELECT score FROM SC WHERE SC.S#=t.S#AND C#='006') AS 英语

        ,COUNT(*) AS 有效课程数, AVG(t.score) AS 平均成绩

    FROM SC AS t

    GROUP BY S#

    ORDER BY avg(t.score) 

18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分

    SELECT L.C# As 课程ID,L.score AS 最高分,R.score AS 最低分

    FROM SC L ,SC AS R

    WHERE L.C# = R.C# and

       L.score = (SELECT MAX(IL.score)

                      FROM SC ASIL,Student AS IM

                      WHERE L.C# =IL.C# and IM.S#=IL.S#

                      GROUP BYIL.C#)

        AND

        R.Score= (SELECT MIN(IR.score)

                      FROM SC ASIR

                      WHERE R.C# =IR.C#

                 GROUP BY IR.C#

                    );

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

    SELECT t.C# AS 课程号,max(course.Cname)AS 课程名,isnull(AVG(score),0) AS平均成绩

        ,100 * SUM(CASE WHEN  isnull(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分数

    FROM SC T,Course

    where t.C#=course.C#

    GROUP BY t.C#

    ORDER BY 100* SUM(CASE WHEN  isnull(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) DESC

20、查询如下课程平均成绩和及格率的百分数(用"1行"显示): 

企业管理（001），马克思（002），OO&UML （003），数据库（004） 

 SELECT SUM(CASE WHEN C# ='001' THEN score ELSE 0 END)/SUM(CASE C# WHEN '001' THEN 1 ELSE 0 END) AS 企业管理平均分

        ,100 * SUM(CASE WHEN C# = '001' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = '001' THEN 1 ELSE 0 END) AS 企业管理及格百分数

        ,SUM(CASE WHEN C# = '002' THEN score ELSE 0 END)/SUM(CASE C# WHEN '002' THEN 1 ELSE 0 END) AS 马克思平均分

        ,100 * SUM(CASE WHEN C# = '002' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = '002' THEN 1 ELSE 0 END) AS 马克思及格百分数

        ,SUM(CASE WHEN C# = '003' THEN score ELSE 0 END)/SUM(CASE C# WHEN '003' THEN 1 ELSE 0 END) AS UML平均分

        ,100* SUM(CASE WHEN C# = '003' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = '003' THEN 1 ELSE 0 END) AS UML及格百分数

        ,SUM(CASE WHEN C# = '004' THEN score ELSE 0 END)/SUM(CASE C# WHEN '004' THEN 1 ELSE 0 END) AS 数据库平均分

        ,100 * SUM(CASE WHEN C# = '004' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = '004' THEN 1 ELSE 0 END) AS 数据库及格百分数

  FROM SC 

21、查询不同老师所教不同课程平均分从高到低显示

  SELECT max(Z.T#) AS 教师ID,MAX(Z.Tname) AS 教师姓名,C.C# AS 课程ＩＤ,MAX(C.Cname) AS 课程名称,AVG(Score) AS 平均成绩 

    FROM SC AS T,Course AS C ,Teacher AS Z 

    where T.C#=C.C# and C.T#=Z.T# 

  GROUP BY C.C# 

  ORDER BY AVG(Score) DESC 

22、查询如下课程成绩第 3 名到第 6 名的学生成绩单：

企业管理（001），马克思（002），UML （003），数据库（004）

[学生ID],[学生姓名],企业管理,马克思,UML,数据库,平均成绩

    SELECT  DISTINCT top 3 

      SC.S# As 学生学号, 

        Student.Sname AS 学生姓名 , 

      T1.score AS 企业管理, 

      T2.score AS 马克思, 

      T3.score AS UML, 

      T4.score AS 数据库, 

      ISNULL(T1.score,0) + ISNULL(T2.score,0) + ISNULL(T3.score,0) + ISNULL(T4.score,0) as 总分 

      FROM Student,SC  LEFT JOIN SC AS T1 

                      ON SC.S# = T1.S# AND T1.C# = '001' 

            LEFT JOIN SC AS T2 

                      ON SC.S# = T2.S# AND T2.C# = '002' 

            LEFT JOIN SC AS T3 

                      ON SC.S# = T3.S# AND T3.C# = '003' 

            LEFT JOIN SC AS T4 

                      ON SC.S# = T4.S# AND T4.C# = '004' 

      WHERE student.S#=SC.S# and 

      ISNULL(T1.score,0) + ISNULL(T2.score,0) + ISNULL(T3.score,0) + ISNULL(T4.score,0) 

      NOT IN 

      (SELECT 

            DISTINCT 

            TOP 15 WITH TIES 

            ISNULL(T1.score,0) + ISNULL(T2.score,0) + ISNULL(T3.score,0) + ISNULL(T4.score,0) 

      FROM sc 

            LEFT JOIN sc AS T1 

                      ON sc.S# = T1.S# AND T1.C# = 'k1' 

            LEFT JOIN sc AS T2 

                      ON sc.S# = T2.S# AND T2.C# = 'k2' 

            LEFT JOIN sc AS T3 

                      ON sc.S# = T3.S# AND T3.C# = 'k3' 

            LEFT JOIN sc AS T4 

                      ON sc.S# = T4.S# AND T4.C# = 'k4' 

      ORDER BY ISNULL(T1.score,0) + ISNULL(T2.score,0) + ISNULL(T3.score,0) + ISNULL(T4.score,0) DESC); 

23、统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]

    SELECT SC.C# as 课程ID, Cname as 课程名称 

        ,SUM(CASE WHEN score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) AS [100 - 85] 

        ,SUM(CASE WHEN score BETWEEN 70 AND 85 THEN 1 ELSE 0 END) AS [85 - 70] 

        ,SUM(CASE WHEN score BETWEEN 60 AND 70 THEN 1 ELSE 0 END) AS [70 - 60] 

        ,SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END) AS [60 -] 

    FROM SC,Course 

    where SC.C#=Course.C# 

    GROUP BY SC.C#,Cname; 

24、查询学生平均成绩及其名次

      SELECT 1+(SELECT COUNT( distinct 平均成绩) 

              FROM (SELECT S#,AVG(score) AS 平均成绩 

                      FROM SC 

                  GROUP BY S# 

                  ) AS T1 

            WHERE 平均成绩 > T2.平均成绩) as 名次, 

      S# as 学生学号,平均成绩 

    FROM (SELECT S#,AVG(score) 平均成绩 

            FROM SC 

        GROUP BY S# 

        ) AS T2 

    ORDER BY 平均成绩 desc; 

25、查询各科成绩前三名的记录:(不考虑成绩并列情况)

      SELECT t1.S# as 学生ID,t1.C# as 课程ID,Score as 分数 

      FROM SC t1 

      WHERE score IN (SELECT TOP 3 score 

              FROM SC 

              WHERE t1.C#= C# 

            ORDER BY score DESC 

              ) 

      ORDER BY t1.C#; 

26、查询每门课程被选修的学生数

  select c#,count(S#) from sc group by C#; 

27、查询出只选修了一门课程的全部学生的学号和姓名

  select SC.S#,Student.Sname,count(C#) AS 选课数 

  from SC ,Student 

  where SC.S#=Student.S# group by SC.S# ,Student.Sname having count(C#)=1;

28、查询男生、女生人数

    Select count(Ssex) as 男生人数 from Student group by Ssex having Ssex='男'; 

    Select count(Ssex) as 女生人数 from Student group by Ssex having Ssex='女'； 

29、查询姓“张”的学生名单

    SELECT Sname FROM Student WHERE Sname like '张%';

30、查询同名同性学生名单，并统计同名人数

  select Sname,count(*) from Student group by Sname having  count(*)>1;

31、1981年出生的学生名单(注：Student表中Sage列的类型是datetime)

    select Sname,  CONVERT(char (11),DATEPART(year,Sage)) as age 

    from student 

    where  CONVERT(char(11),DATEPART(year,Sage))='1981'; 

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 C#,Avg(score) from SC group by C# order by Avg(score),C# DESC ;

33、查询平均成绩大于85的所有学生的学号、姓名和平均成绩

    select Sname,SC.S# ,avg(score) 

    from Student,SC 

    where Student.S#=SC.S# group by SC.S#,Sname having    avg(score)>85;

34、查询课程名称为“数据库”，且分数低于60的学生姓名和分数

    Select Sname,isnull(score,0) 

    from Student,SC,Course 

    where SC.S#=Student.S# and SC.C#=Course.C# and  Course.Cname='数据库'and score <60;

35、查询所有学生的选课情况；

    SELECT SC.S#,SC.C#,Sname,Cname 

    FROM SC,Student,Course 

    where SC.S#=Student.S# and SC.C#=Course.C# ;

36、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  distinct student.S#,student.Sname,SC.C#,SC.score 

    FROM student,Sc 

    WHERE SC.score>=70 AND SC.S#=student.S#; 

37、查询不及格的课程，并按课程号从大到小排列

    select c# from sc where scor e <60 order by C# ;

38、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名；

    select SC.S#,Student.Sname from SC,Student where SC.S#=Student.S# and Score>80 and C#='003';

39、求选了课程的学生人数

     select count( *) from sc; 

40、查询选修“叶平”老师所授课程的学生中，成绩最高的学生姓名及其成绩

    select Student.Sname,score 

    from Student,SC,Course C,Teacher 

    where Student.S#=SC.S# and SC.C#=C.C# and C.T#=Teacher.T# and Teacher.Tname='叶平' and SC.score=(select max(score)from SC where C#=C.C# ); 

41、查询各个课程及相应的选修人数

    select count(*) from sc group by C#; 

42、查询不同课程成绩相同的学生的学号、课程号、学生成绩

  select distinct  A.S#,B.score from SC A  ,SC B where A.Score=B.Score and A.C# <>B.C# ; 

43、查询每门功成绩最好的前两名

    SELECT t1.S# as 学生ID,t1.C# as 课程ID,Score as 分数 

      FROM SC t1 

      WHERE score IN (SELECT TOP 2 score 

              FROM SC 

              WHERE t1.C#= C# 

            ORDER BY score DESC 

              ) 

      ORDER BY t1.C#; 

44、统计每门课程的学生选修人数（超过10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，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# as 课程号,count(*) as 人数 

    from  sc  

    group  by  C# 

    order  by  count(*) desc,c#  

45、检索至少选修两门课程的学生学号

    select  S#  

    from  sc  

    group  by  s# 

    having  count(*)  >  =  2 

46、查询全部学生都选修的课程的课程号和课程名

    select  C#,Cname  

    from  Course  

    where  C#  in  (select  c#  from  sc group  by  c#)  

47、查询没学过“叶平”老师讲授的任一门课程的学生姓名

    select Sname from Student where S# not in (select S# from Course,Teacher,SC where Course.T#=Teacher.T# and SC.C#=course.C# and Tname='叶平'); 

48、查询两门以上不及格课程的同学的学号及其平均成绩

    select S#,avg(isnull(score,0)) from SC where S# in (select S# from SC where score <60 group by S# having count(*)>2)group by S#; 

49、检索“004”课程分数小于60，按分数降序排列的同学学号

    select S# from SC where C#='004'and score <60 order by score desc; 

50、删除“002”同学的“001”课程的成绩

delete from Sc where S# = '001' and C# = '001';