2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；

select a.student_id from(select * from score where course_id = (select course_id from course where course_name = '生物'))as a inner join(select * from score where course_id = (select course_id from course where course_name = '物理'))as b on a.student_id = b.student_id and a.score_number > b.score_number;

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

4、查询所有同学的学号、姓名、选课数、总成绩；

select a.student_id,a.student_name,count(course_id),ifnull(sum(score_number),0) from student as a left join score as b on a.student_id = b.student_id group by a.student_id

5、查询姓“马”的老师的个数；

select count(*) from teacher where teacher_name like '马%'

6、查询没学过“俞敏洪”老师课的同学的学号、姓名；

select student_id,student_name from student where student_id not in (select student_id from score natural join course where teacher_id = (select teacher_id from teacher where teacher_name = '马化腾'))

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 student_id,student_name from student where student_id in (select  student_id from score group by student_id having group_concat(course_id) like '1,2%') ;

8、查询学过“马云”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；

21、查询每门课程的任课老师、课程名称和课程平均分，并按照分数从高到低排序；

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、查询选修了课程的学生人数

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、查询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；

39、查询两门以上不及格课程的同学的学号及其平均成绩；

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