mysql初学者的一套简单练习题（表和答案）想练习sql语句必备哦！

1.这里面的表是我自己创的，可能有些bug，发现问题，可以找我啊！必回！
2.答案有问题可以和我交流啊
3.我也是初学者，有小白愿意交流也可以找我。
4.一起进步




以下是题目以及答案

2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
    SELECT * FROM
        (SELECT score.student_id,course.cname,score.num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="生物") AS A
     INNER JOIN 
        (SELECT score.student_id,course.cname,score.num FROM score LEFT JOIN course on score.course_id=course.cid WHERE course.cname="物理") AS B
        on A.student_id = B.student_id WHERE A.num > B.num;
        
3、查询平均成绩大于60分的同学的学号和平均成绩；
    SELECT B.student_id,student.sname,B.s_num FROM (SELECT student_id,avg(num) AS s_num from score GROUP BY student_id HAVING s_num>60) as B
        LEFT JOIN student on B.student_id = student.sid;  取前三： %ORDER BY s_num desc LIMIT 3;

4、查询所有同学的学号、姓名、选课数、总成绩；
    SELECT score.student_id,student.sname,COUNT(score.course_id) AS courses,SUM(num) as T_Score 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 * from teacher WHERE tname like "李%";
    
6、查询没学过“李平”老师课的同学的学号、姓名；
    SELECT student.sid,student.sname FROM student WHERE student.sid NOT IN (
        SELECT score.student_id FROM score LEFT JOIN course ON score.course_id = course.cid WHERE score.course_id IN (
            SELECT course.cid FROM course LEFT JOIN teacher ON course.teacher_id = teacher.tid WHERE teacher.tname LIKE "李平%") GROUP BY score.student_id)
    
7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
    SELECT B.sid,B.sname FROM(
        SELECTstudent.sid,score.course_id,student.sname FROM score
            LEFT JOIN student ON score.student_id = student.sid WHERE score.course_id BETWEEN 1 AND 2) AS B
        GROUP BY B.sid HAVING COUNT(B.course_id)=2;

8、查询学过“叶平”老师所教的所有课的同学的学号、姓名；
    SELECT student.sid,student.sname 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 LIKE "李平%") 
            GROUP BY student.sid HAVING COUNT(student_id)=2;

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；
    SELECT A.sid,A.sname,A.num as score_2,B.num as score_1 FROM
        (SELECT student.sid,student.sname,score.num FROM score LEFT JOIN student on score.student_id=student.sid WHERE score.course_id=2) AS A
        INNER JOIN
        (SELECT student.sid,student.sname,score.num FROM score LEFT JOIN student on score.student_id=student.sid WHERE score.course_id=1) AS B
            ON A.sid = B.sid WHERE A.num60 GROUP BY course_id) as B ON A.cid=B.course_id ORDER BY 及格率 DESC;
    整合：
    SELECT x.课程ID,x.课程名,x.平均分,xx.及格率 FROM
    (SELECT score.course_id AS 课程ID,course.cname as 课程名,AVG(num) AS 平均分 FROM score 
            LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id ORDER BY 平均分 ASC) AS x 
    LEFT JOIN
    (SELECT A.cid,A.cname,ROUND(B.s/A.ss*100,1) AS 及格率 FROM
        (SELECT cid,cname,COUNT(course_id) AS ss FROM score LEFT JOIN course ON score.course_id=course.cid GROUP BY course_id) as A
            INNER JOIN
        (SELECT course_id,COUNT(num) as s FROM score WHERE score.num>60 GROUP BY course_id) as B ON A.cid=B.course_id ORDER BY 及格率 DESC) AS xx
ON x.课程ID=xx.cid 
    
    标准：
    SELECT course_id,AVG(num) AS 平均分,ROUND(sum(CASE WHEN num<60 then 0 ELSE 1 END)/sum(1)*100,1) AS 及格率 
        FROM score GROUP BY course_id ORDER BY 平均分 ASC,及格率 DESC;


20、课程平均分从高到低显示（现实任课老师）；
    SELECT course.cname,teacher.tname,xxx.平均分 FROM course
        LEFT JOIN teacher ON course.teacher_id=teacher.tid 
        LEFT JOIN (SELECT course_id,AVG(num) AS 平均分 FROM score GROUP BY course_id) AS xxx ON xxx.course_id=course.cid
        ORDER BY xxx.平均分 DESC

21、查询各科成绩前三名的记录:(不考虑成绩并列情况) 
    SELECT s1.cid AS 课程ID,s1.cname AS 课程,
        (SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 0,1) AS 第一,
        (SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 1,1) AS 第二,
        (SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 2,1) AS 第三
    FROM course AS s1    
        
22、查询每门课程被选修的学生数；
    SELECT course.cid AS 课程ID,course.cname AS 课程名,COUNT(1) AS 学生数 FROM score 
        LEFT JOIN course ON score.course_id=course.cid GROUP BY score.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 AS 学号,student.sname AS 姓名 FROM student
        WHERE sid IN (SELECT student_id FROM score GROUP BY student_id HAVING count(1)=1)    
        
24、查询男生、女生的人数；
    SELECT gender AS 性别,COUNT(1) AS 人数 FROM student GROUP BY gender;

25、查询姓“张”的学生名单；
    SELECT * 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 As 姓名,COUNT(1) AS 人数 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.cid AS 课程ID,
        course.cname AS 课程名,
        AVG(IF(ISNULL(num),0,score.num)) AS 平均分
    FROM score LEFT JOIN course ON score.course_id = course.cid 
        GROUP BY score.course_id ORDER BY 平均分 ASC,课程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.sid AS 学号,student.sname AS 姓名,AVG(if(isnull(num),0,score.num)) AS 平均分 
    FROM score LEFT JOIN student ON score.student_id=student.sid 
        GROUP BY score.student_id HAVING 平均分>85;
    
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.sid AS 学号,student.sname AS 姓名,score.num AS 成绩 FROM score 
        LEFT JOIN course ON score.course_id=course.cid
        LEFT JOIN student ON score.student_id= student.sid
            WHERE course.cname="数学" AND score.num<60；

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 student.sid AS 学号,student.sname AS 姓名 FROM student WHERE sid IN 
        (SELECT student_id FROM score WHERE score.course_id =3 AND num > 80) 

31、求选了课程的学生人数
    SELECT COUNT(A.student_id) AS 总人数 
        FROM (SELECT student_id FROM score GROUP BY student_id) AS A

    SELECT COUNT(DISTINCT student_id) AS 总人数 FROM score;
    
32、查询选修“杨艳”老师(这个老师没有，就以张磊老师举例)所授课程的学生中，成绩最高的学生姓名及其成绩；
    SELECT student.sid AS 学号,student.sname AS 姓名,num AS 成绩 FROM score 
        LEFT JOIN course ON score.course_id=course.cid
        LEFT JOIN student ON score.student_id=student.sid
        LEFT JOIN teacher ON course.teacher_id=teacher.tid
            WHERE teacher.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_id AS ID,course.cname AS 课程,count(1) AS 人数 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.student_id,s1.course_id,s1.num FROM score AS s1,score AS s2
        WHERE s1.student_id    != s2.student_id AND s1.course_id!=s2.course_id AND s1.num=s2.num 

35、查询每门课程成绩最好的前两名；
    SELECT cid AS 课程ID,cname AS 课程,
        (SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 0,1) AS 第一,
        (SELECT num FROM score AS s2 WHERE s2.course_id=s1.cid GROUP BY num ORDER BY num DESC LIMIT 1,1) AS 第二
    FROM course AS s1

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(course_id)>=2

37、查询全部学生都选修的课程的课程号和课程名；
    SELECT course.cid AS 课程号,course.cname AS 课程名 FROM score 
        LEFT JOIN course ON score.course_id=course.cid GROUP BY score.course_id
            HAVING COUNT(student_id)=(SELECT COUNT(sid) FROM student)

38、查询没学过“李平”老师讲授的任一门课程的学生姓名；
    SELECT student.sid,student.sname FROM student
        WHERE student.sid not IN (SELECT student_id FROM score 
            WHERE course_id IN(SELECT cid FROM course 
                LEFT JOIN teacher ON course.teacher_id=teacher.tid 
                    WHERE teacher.tname="李平老师" ) 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 score.student_id AS 学号,student.sname AS 姓名,
    (SELECT AVG(if(ISNULL(A.num),0,A.num)) FROM score AS A
        WHERE A.student_id IN (SELECT student_id FROM score WHERE num<60 
            GROUP BY student_id HAVING COUNT(1)>=2)) AS 平均成绩 
    FROM score LEFT JOIN student ON score.student_id=student.sid 
        WHERE num<60 GROUP BY student_id HAVING COUNT(1)>2
    
标准：    
    SELECT student_id AS 学号,sname AS 姓名,AVG(num) AS 平均成绩 FROM score
    LEFT JOIN student ON score.student_id=student.sid
        WHERE student_id IN (SELECT student_id FROM score 
            WHERE num<60 GROUP BY student_id HAVING COUNT(1)>=2) 
                GROUP BY student_id
        
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,num FROM score 
        WHERE score.course_id=4 AND num <60 ORDER BY num ASC

41、删除“002”同学的“001”课程的成绩；
    delete from score where student_id=2 and corse_id=1;