必看，经典sql面试题2（学生表_课程表_成绩表_教师表）

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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;