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,tyfrom(select student_id,num as swfrom score left join course on score.course_id = course.cid where course.cname = '生物') as A

left join

(select student_id,num as tyfrom 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.snamefromscore left join student on score.student_id=student.sid

group by score.student_id5、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 B6、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_idfrom score where score.course_id in(

select cidfrom 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,snamefrom(select student_id,course_idfrom 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,snamefrom student where sid in(

select distinct student_idfrom 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,snamefrom score left join student on score.student_id =student.sid

group by student_id HAVING count(course_id)= (select count(1) fromcourse)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_id13、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,snamefrom score left join student on score.student_id = student.sid where student_id in(

select student_idfrom 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；

deletefrom score where course_id in(

select cidfrom 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,x2fromtb2;

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_idfrom 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 numfrom 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 numfrom 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 numfrom 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)fromscore as sc

group by student_id desc18、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_numfromscore 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 fromscore 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 fromcourse

left join score on course.cid=score.course_id

left join teacher on course.teacher_id=teacher.tid

group by score.course_id21、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_numfromscore left join

(

select

sid,

(select numfrom score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,

(select numfrom score as s2 where s2.course_id = s1.course_id order by num desc limit 3,1) as second_numfromscore as s1

) as T

on score.sid=T.sid

where score.num<= T.first_num and score.num >=T.second_num22、查询每门课程被选修的学生数；

select course_id, count(1) fromscore 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) fromscore

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 B25、查询姓“张”的学生名单；

select snamefrom 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 fromstudent 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 fromscore 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.numfromscore

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)fromscore

select count(c)from(

select count(student_id) as cfromscore group by student_id) as A32、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,numfromscore

left join student on score.student_id=student.sid

where score.course_idin (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) fromscore

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.numfrom 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_numfromscore left join

(

select

sid,

(select numfrom score as s2 where s2.course_id = s1.course_id order by num desc limit 0,1) as first_num,

(select numfrom score as s2 where s2.course_id = s1.course_id order by num desc limit 1,1) as second_numfromscore as s1

) as T

on score.sid=T.sid

where score.num<= T.first_num and score.num >=T.second_num36、检索至少选修两门课程的学生学号；

select student_idfrom 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) fromstudent);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.snamefromscore

left join student on score.student_id=student.sid

where score.course_idnot in(

select cidfrom course left join teacher on course.teacher_id = teacher.tid where tname = '张磊老师')

group by student_id39、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_idfrom score where num< 60 and course_id = 4order by num desc;41、删除“002”同学的“001”课程的成绩；

deletefrom score where course_id = 1 and student_id = 2