数据库多表查询之练习

CREATE DATABASE javacto;
USE javacto;

#班级表
CREATE TABLE class(
	cid INT PRIMARY KEY,
	caption VARCHAR(6)
);

#老师表:teacher
CREATE TABLE teacher(
	tid INT PRIMARY KEY,
	tname VARCHAR(8) NOT NULL
);
#学生表
CREATE TABLE student(
	sid INT PRIMARY KEY,
	sname VARCHAR(8) NOT NULL,
	gender VARCHAR(2) NOT NULL,
	class_id INT NOT NULL
);

#课程表 course

CREATE TABLE course(
	cid INT PRIMARY KEY,
	cname VARCHAR(8) NOT NULL,
	teacher_id INT NOT NULL,
	FOREIGN KEY(teacher_id) REFERENCES teacher(tid)
);


#成绩表
CREATE TABLE score(
	sid  INT PRIMARY KEY,
	student_id INT NOT NULL,
	scorse_id INT NOT NULL,
	number INT NOT NULL,
	FOREIGN KEY(student_id) REFERENCES student(sid),
	FOREIGN KEY(scorse_id) REFERENCES course(cid)
);

#建库建表

数据库多表查询之练习_第1张图片


1、自行创建测试数据

2、查询“生物”课程比“物理”课程成绩高的所有学生的学号;

3、查询平均成绩大于60分的同学的学号和平均成绩; 

  SELECT student_id,AVG(number) FROM score GROUP BY student_id HAVING AVG(number)>60;

  问题:很明显是平均之后进行比较(用HAVING),出现HAVING之后必须在前有GROUP BY;

4、查询所有同学的学号、姓名、选课数、总成绩;

  SELECT student.sid,student.sname,COUNT(scorse_id),SUM(number)FROM student LEFT JOIN score ON student.sid=score.student_id GROUP BY student.sid

5、查询姓“李”的老师的个数;

  问题:LIKE模糊匹配不清楚

  SELECT COUNT(tid) FROM teacher WHERE tname LIKE '李%';

6、查询没学过“叶平”老师课的同学的学号、姓名;

7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名;

8、查询学过“叶平”老师所教的所有课的同学的学号、姓名;

9、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;

10、查询有课程成绩小于60分的同学的学号、姓名;

11、查询没有学全所有课的同学的学号、姓名;

12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名;

13、查询至少学过学号为“001”同学所选课程中任意一门课的其他同学学号和姓名;

14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名;

15、删除学习“叶平”老师课的SC表记录;

16、向SC表中插入一些记录,这些记录要求符合以下条件:①没有上过编号“002”课程的同学学号;②插入“002”号课程的平均成绩; 

17、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分;

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;

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;

20、课程平均分从高到低显示(现实任课老师);

21、查询各科成绩前三名的记录:(不考虑成绩并列情况) 

22、查询每门课程被选修的学生数;

23、查询出只选修了一门课程的全部学生的学号和姓名;

24、查询男生、女生的人数;

25、查询姓“张”的学生名单;

26、查询同名同姓学生名单,并统计同名人数;

27、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;

28、查询平均成绩大于85的所有学生的学号、姓名和平均成绩;

29、查询课程名称为“数学”,且分数低于60的学生姓名和分数;

30、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; 

31、求选了课程的学生人数

32、查询选修“杨艳”老师所授课程的学生中,成绩最高的学生姓名及其成绩;

33、查询各个课程及相应的选修人数;

34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩;

35、查询每门课程成绩最好的前两名;

36、检索至少选修两门课程的学生学号;

37、查询全部学生都选修的课程的课程号和课程名;

38、查询没学过“叶平”老师讲授的任一门课程的学生姓名;

39、查询两门以上不及格课程的同学的学号及其平均成绩;

40、检索“004”课程分数小于60,按分数降序排列的同学学号;

41、删除“002”同学的“001”课程的成绩;

更多学习资料:javacto.taobao.com

#答案下面  


2、查询“生物”课程比“物理”课程成绩高的所有学生的学号;
思路:
    获取所有有生物课程的人(学号,成绩) - 临时表
    获取所有有物理课程的人(学号,成绩) - 临时表
    根据【学号】连接两个临时表:
        学号  物理成绩   生物成绩

    然后再进行筛选

        SELECT A.student_id,sw,ty FROM 

        (SELECT student_id,num AS sw FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = '生物') AS A

        LEFT JOIN 

        (SELECT student_id,num  AS ty FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = '体育') AS B

        ON A.student_id = B.student_id WHERE sw > IF(ISNULL(ty),0,ty);

3、查询平均成绩大于60分的同学的学号和平均成绩; 
    思路:
        根据学生分组,使用AVG获取平均值,通过HAVING对AVG进行筛选

        SELECT student_id,AVG(num) FROM score GROUP BY student_id HAVING AVG(num) > 60

4、查询所有同学的学号、姓名、选课数、总成绩;

    SELECT score.student_id,SUM(score.num),COUNT(score.student_id),student.sname 
    FROM 
        score LEFT JOIN student ON score.student_id = student.sid   
    GROUP BY score.student_id

5、查询姓“李”的老师的个数;
    SELECT COUNT(tid) FROM teacher WHERE tname LIKE '李%'

    SELECT COUNT(1) FROM (SELECT tid FROM teacher WHERE tname LIKE '李%') AS B

6、查询没学过“叶平”老师课的同学的学号、姓名;
    思路:
        先查到“李平老师”老师教的所有课ID
        获取选过课的所有学生ID
        学生表中筛选
    SELECT * FROM student WHERE sid NOT IN (
        SELECT DISTINCT student_id FROM score WHERE score.course_id IN (
            SELECT cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE tname = '李平老师'
        )
    )

7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名;
    思路:
        先查到既选择001又选择002课程的所有同学
        根据学生进行分组,如果学生数量等于2表示,两门均已选择

    SELECT student_id,sname FROM 

    (SELECT student_id,course_id FROM score WHERE course_id = 1 OR course_id = 2) AS B
     
    LEFT JOIN student ON B.student_id = student.sid GROUP BY student_id HAVING COUNT(student_id) > 1


8、查询学过“叶平”老师所教的所有课的同学的学号、姓名;

    同上,只不过将001和002变成 IN (叶平老师的所有课)

9、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;
    同第1题


10、查询有课程成绩小于60分的同学的学号、姓名;
        
    SELECT sid,sname FROM student WHERE sid IN (
        SELECT DISTINCT student_id FROM score WHERE num < 60
    )

11、查询没有学全所有课的同学的学号、姓名;
    思路:
        在分数表中根据学生进行分组,获取每一个学生选课数量
        如果数量 == 总课程数量,表示已经选择了所有课程

        SELECT student_id,sname 
        FROM score LEFT JOIN student ON score.student_id = student.sid 
        GROUP BY student_id HAVING COUNT(course_id) = (SELECT COUNT(1) FROM course)


12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名;
    思路:
        获取 001 同学选择的所有课程
        获取课程在其中的所有人以及所有课程
        根据学生筛选,获取所有学生信息
        再与学生表连接,获取姓名

        SELECT student_id,sname, COUNT(course_id) 
        FROM score LEFT JOIN student ON score.student_id = student.sid
        WHERE student_id != 1 AND course_id IN (SELECT course_id FROM score WHERE student_id = 1) GROUP BY student_id

13、查询至少学过学号为“001”同学所有课的其他同学学号和姓名;
        先找到和001的学过的所有人
        然后个数 = 001所有学科     ==》 其他人可能选择的更多

        SELECT student_id,sname, COUNT(course_id) 
        FROM score LEFT JOIN student ON score.student_id = student.sid
        WHERE student_id != 1 AND course_id IN (SELECT course_id FROM score WHERE student_id = 1) GROUP BY student_id HAVING COUNT(course_id) = (SELECT COUNT(course_id) FROM score WHERE student_id = 1)

14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名;
        
        个数相同
        002学过的也学过

        SELECT student_id,sname FROM score LEFT JOIN student ON score.student_id = student.sid WHERE student_id IN (
            SELECT student_id FROM score  WHERE student_id != 1 GROUP BY student_id HAVING COUNT(course_id) = (SELECT COUNT(1) FROM score WHERE student_id = 1)
        ) AND course_id IN (SELECT course_id FROM score WHERE student_id = 1) GROUP BY student_id HAVING COUNT(course_id) = (SELECT COUNT(1) FROM score WHERE student_id = 1)


15、删除学习“叶平”老师课的score表记录;

    DELETE FROM score WHERE course_id IN (
        SELECT cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.name = '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:①没有上过编号“002”课程的同学学号;②插入“002”号课程的平均成绩; 
    思路:
        由于INSERT 支持  
                inset INTO tb1(xx,xx) SELECT x1,x2 FROM tb2;
        所有,获取所有没上过002课的所有人,获取002的平均成绩

    INSERT INTO score(student_id, course_id, num) SELECT sid,2,(SELECT AVG(num) FROM score WHERE course_id = 2) 
    FROM student WHERE sid NOT IN (
        SELECT student_id FROM score WHERE course_id = 2
    )
    
17、按平均成绩从低到高 显示所有学生的“语文”、“数学”、“英语”三门的课程成绩,按如下形式显示: 学生ID,语文,数学,英语,有效课程数,有效平均分;
    SELECT sc.student_id,
        (SELECT num FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = "生物" AND score.student_id=sc.student_id) AS sy,
        (SELECT num FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = "物理" AND score.student_id=sc.student_id) AS wl,
        (SELECT num FROM score LEFT JOIN course ON score.course_id = course.cid WHERE course.cname = "体育" AND score.student_id=sc.student_id) AS ty,
        COUNT(sc.course_id),
        AVG(sc.num)
    FROM score AS sc
    GROUP BY student_id DESC         

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 course_id, MAX(num) AS max_num, MIN(num) AS min_num FROM score GROUP BY course_id;

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;
    思路:CASE WHEN .. THEN
    SELECT course_id, AVG(num) AS avgnum,SUM(CASE WHEN score.num > 60 THEN 1 ELSE 0 END)/COUNT(1)*100 AS percent FROM score GROUP BY course_id ORDER BY avgnum ASC,percent DESC;

20、课程平均分从高到低显示(现实任课老师);

    SELECT AVG(IF(ISNULL(score.num),0,score.num)),teacher.tname FROM course 
    LEFT JOIN score ON course.cid = score.course_id 
    LEFT JOIN teacher ON course.teacher_id = teacher.tid

    GROUP BY score.course_id


21、查询各科成绩前三名的记录:(不考虑成绩并列情况) 
    SELECT score.sid,score.course_id,score.num,T.first_num,T.second_num FROM score LEFT JOIN 
    (
    SELECT 
        sid,
        (SELECT num FROM score AS s2 WHERE s2.course_id = s1.course_id ORDER BY num DESC LIMIT 0,1) AS first_num,
        (SELECT num FROM score AS s2 WHERE s2.course_id = s1.course_id ORDER BY num DESC LIMIT 3,1) AS second_num
    FROM 
        score AS s1
    ) AS T
    ON score.sid =T.sid
    WHERE score.num <= T.first_num AND score.num >= T.second_num

22、查询每门课程被选修的学生数;
    
    SELECT course_id, COUNT(1) FROM score GROUP BY course_id;

23、查询出只选修了一门课程的全部学生的学号和姓名;
    SELECT student.sid, student.sname, COUNT(1) FROM score

    LEFT JOIN student ON score.student_id  = student.sid

     GROUP BY course_id HAVING COUNT(1) = 1


24、查询男生、女生的人数;
    SELECT * FROM 
    (SELECT COUNT(1) AS man FROM student WHERE gender='男') AS A ,
    (SELECT COUNT(1) AS feman FROM student WHERE gender='女') AS B 

25、查询姓“张”的学生名单;
    SELECT sname FROM student WHERE sname LIKE '张%';

26、查询同名同姓学生名单,并统计同名人数;

    SELECT sname,COUNT(1) AS COUNT FROM student GROUP BY sname;

27、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 course_id,AVG(IF(ISNULL(num), 0 ,num)) AS AVG FROM score GROUP BY course_id ORDER BY AVG     ASC,course_id DESC;

28、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 student_id,sname, AVG(IF(ISNULL(num), 0 ,num)) FROM score LEFT JOIN student ON score.student_id = student.sid GROUP BY student_id;

29、查询课程名称为“数学”,且分数低于60的学生姓名和分数;

    SELECT student.sname,score.num FROM score 
    LEFT JOIN course ON score.course_id = course.cid
    LEFT JOIN student ON score.student_id = student.sid
    WHERE score.num < 60 AND course.cname = '生物'

30、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 * FROM score WHERE score.student_id = 3 AND score.num > 80

31、求选了课程的学生人数

    SELECT COUNT(DISTINCT student_id) FROM score

    SELECT COUNT(c) FROM (
        SELECT COUNT(student_id) AS c FROM score GROUP BY student_id) AS A

32、查询选修“杨艳”老师所授课程的学生中,成绩最高的学生姓名及其成绩;
    
    SELECT sname,num FROM score 
    LEFT JOIN student ON score.student_id = student.sid
    WHERE score.course_id IN (SELECT course.cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE tname='张磊老师') ORDER BY num DESC LIMIT 1;

33、查询各个课程及相应的选修人数;
    SELECT course.cname,COUNT(1) FROM score
    LEFT JOIN course ON score.course_id = course.cid
    GROUP BY course_id;


34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩;
    SELECT DISTINCT s1.course_id,s2.course_id,s1.num,s2.num FROM score AS s1, score AS s2 WHERE s1.num = s2.num AND s1.course_id != s2.course_id;

35、查询每门课程成绩最好的前两名;

    SELECT score.sid,score.course_id,score.num,T.first_num,T.second_num FROM score LEFT JOIN 
    (
    SELECT 
        sid,
        (SELECT num FROM score AS s2 WHERE s2.course_id = s1.course_id ORDER BY num DESC LIMIT 0,1) AS first_num,
        (SELECT num FROM score AS s2 WHERE s2.course_id = s1.course_id ORDER BY num DESC LIMIT 1,1) AS second_num
    FROM 
        score AS s1
    ) AS T
    ON score.sid =T.sid
    WHERE score.num <= T.first_num AND score.num >= T.second_num

36、检索至少选修两门课程的学生学号;
    SELECT student_id FROM score GROUP BY student_id HAVING COUNT(student_id) > 1

37、查询全部学生都选修的课程的课程号和课程名;
    SELECT course_id,COUNT(1) FROM score GROUP BY course_id HAVING COUNT(1) = (SELECT COUNT(1) FROM student);

38、查询没学过“叶平”老师讲授的任一门课程的学生姓名;
    SELECT student_id,student.sname FROM score 
    LEFT JOIN student ON score.student_id = student.sid
    WHERE score.course_id NOT IN (
        SELECT cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE tname = '张磊老师'
    ) 
    GROUP BY student_id

39、查询两门以上不及格课程的同学的学号及其平均成绩;

    SELECT student_id,COUNT(1) FROM score WHERE num < 60 GROUP BY student_id HAVING COUNT(1) > 2

40、检索“004”课程分数小于60,按分数降序排列的同学学号;
    SELECT student_id FROM score WHERE num< 60 AND course_id = 4 ORDER BY num DESC;

41、删除“002”同学的“001”课程的成绩;
    DELETE FROM score WHERE course_id = 1 AND student_id = 2

更多学习资料:javacto.taobao.com

 

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