1、自行创建测试数据
略...
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 score.sid,score.student_id,course.cname,score.number from score left join course on course.cid = score.course_id where course.cname = '生物') as A
inner join
(select score.sid,score.student_id,course.cname,score.number from score left join course on course.cid = score.course_id where course.cname = '物理') as B
on A.student_id = B.student_id
where A.number > B.number;
3、查询平均成绩大于60分的同学的学号、学生姓名和平均成绩；
select B.student_id,B.a,student.sname from (select student_id,avg(number) as a from score group by student_id having avg(number) > 60) as B left join student on B.student_id = student.sid;
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(1) as course_num,sum(number) as scorce_total from score left join student on score.student_id = student.sid group by student_id;
5、查询姓“李”的老师的个数；
select count(1) 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；
select sid,sname from student where sid not in (
select distinct student_id from score
where course_id in (
select course.cid from course
left join teacher on course.teacher_id = teacher.tid
where tname = '叶平'
)
);
7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
方法一：
select * from
(select student_id,sname from score
left join student on score.student_id = student.sid
where course_id = 1) as a
where student_id in
(
select student_id from score
left join student on score.student_id = student.sid
where course_id = 2
) ;
方法二：
select A.student_id,B.sname from score as A left join
student as B on A.student_id = B.sid
where course_id = 1 or course_id = 2
group by student_id having count(1) > 1;
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_id,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 = '叶平') group by student_id having count(1) =
(select count(1) from course
left join teacher on course.teacher_id = teacher.tid
where tname = '叶平' group by teacher_id);
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.student_id,student.sname from
(select number as num1,student_id from score where course_id = 1) as A
inner join
(select number as num2,student_id from score where course_id = 2) as B on A.student_id = B.student_id
left join
student on A.student_id = student.sid
where A.num1 > B.num2;
10、查询有课程成绩小于60分的同学的学号、姓名；
select distinct student_id,sname from score
left join student on score.student_id = student.sid
where number < 60;
distinct 效率不高 尽量用 group by
11、查询没有学全所有课的同学的学号、姓名；
select * from score group by student_id
having count(1) <
(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；
select distinct student_id,sname from score
left join student on score.student_id = student.sid
where course_id in (select course_id from score where student_id = 1) and student_id != 1;
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；
select student_id from
score
left join student on score.student_id = student.sid
where course_id in (select course_id from score where student_id = 1)
group by student_id having score.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；
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 != 2 group by student_id having count(1) = (select count(1) from score where student_id = 2)) and course_id in (select course_id from score where student_id = 2) group by student_id having count(1) = (select count(1) from score where student_id = 2);
15、删除学习“叶平”老师课的score表记录；
select * from score where course_id in (
select course.cid from course left join teacher on
course.teacher_id = teacher.tid where teacher.tname = '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；
create table SC (
sid int not null auto_increment primary key,
student_id int not null,
course_id int not null,
number int not null,
constraint fk_SC_student foreign key (student_id) references student(sid),
constraint fk_SC_course foreign key (course_id) references course(cid)
)engine=innodb default charset=utf8;
insert into SC(student_id,course_id,number)
select student_id as Sid,2 as Cid,(select avg(number) from score where course_id = 2) as avg_num 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 s1.student_id,
(select number from score as s2 where s2.student_id = s1.student_id and course_id = 1) as 语文,
(select number from score as s2 where s2.student_id = s1.student_id and course_id = 2) as 数学,
(select number from score as s2 where s2.student_id = s1.student_id and course_id = 3) as 英语,
count(1) as 有效课程数,
avg(number) as 平均分
from score as s1 group by student_id;
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 as '课程ID',max(number) as '最高分',min(number) as '最低分' 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；
select T1.course_id,T2.avg_num,T1.num1/T2.num2 as 及格率 from
(select count(1) as num1,sid,course_id from score where number >= 60 group by course_id) as T1
left join
(select count(1) as num2,avg(number) as avg_num,sid from score group by course_id) as T2
on T1.sid = T2.sid order by T2.avg_num desc,T1.num1/T2.num2 desc;
select course_id,avg(number) as avg_num,sum(case when number < 60 then 0 else 1 end)/sum(1) as 及格率 from score group by course_id
order by avg_num desc,及格率 desc;
case when condition then value1 else vlaue2 end
20、课程平均分从高到低显示（显示任课老师）；
select avg(number) from score
left join course on score.course_id = course.cid
left join teacher on course.teacher_id = teacher.tid
group by course_id order by avg(number) desc;
21、查询各科成绩前三名的记录:(不考虑成绩并列情况)
select score.course_id,score.number from score left join (
select sid,(select number from score as S2 where S2.course_id = S1.course_id order by number desc limit 0,1) as first_number,(select number from score as S2 where S2.course_id = S1.course_id order by number desc limit 3,1) as second_number from score as S1
) as T on score.sid = T.sid where score.number > T.second_number and score.number <= T.first_number;
22、查询每门课程被选修的学生数；
select course_id,count(1) as student_num 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 score.student_id,sname from score left join student on score.student_id = student.sid group by student_id having count(1)=1;
24、查询男生、女生的人数；
select count(1),gender 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,count(1) from student group by sname having count(1)>1;
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(number) as a from score group by course_id order by a 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 score.student_id,student.sname,avg(number) from score left join student on score.student_id = student.sid group by student_id having avg(number) > 85;
29、查询课程名称为“物理”，且分数低于60的学生姓名和分数；
select student.sname,score.number from score
left join student on score.student_id = student.sid
left join course on score.course_id = course.cid
where cname='物理' and score.number < 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.sname,score.student_id from score
left join student on score.student_id = student.sid
where score.number>80 and score.course_id=3;
31、求选了课程的学生人数
select count(1) from (select distinct student_id from score) 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 max(number),sname from score
left join course on score.course_id = course.cid
left join teacher on course.teacher_id = teacher.tid
left join student on score.student_id = student.sid
where tname='杨艳';
33、查询各个课程及相应的选修人数；
select course_id,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 T1.student_id,T1.course_id,T2.student_id,T2.course_id,T1.number from score as T1,score as T2 where T1.course_id != T2.course_id and T1.number = T2.number and T1.sid != T2.sid;
35、查询每门课程成绩最好的前两名；
select score.course_id,score.student_id,Temp.first_number,Temp.second_number from
(
select sid,(select number from score as s1 where s1.course_id = T.course_id order by number desc limit 0,1) as first_number,(select number from score as s1 where s1.course_id = T.course_id order by number desc limit 1,1) as second_number from score as T
) as Temp left join score on Temp.sid = score.sid where score.number >= Temp.second_number and score.number <= Temp.first_number ;
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(1) > 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,cname from score
left join course on score.course_id = course.cid
group by course_id having count(1) = (select count(1) from course);
38、查询没学过“叶平”老师讲授的任一门课程的学生姓名；
select sname from student where sid not in
(
select distinct student_id from score where course_id in
(
select course.cid from course left join teacher on course.teacher_id = teacher.tid where tname = '叶平'
)
);
39、查询两门以上不及格课程的同学的学号、姓名及其平均成绩；
select student_id,avg(number),sname from score left join student on score.student_id = student.sid where number < 60 group by student_id having count(1) > 1;
40、检索“003”课程分数小于60，按分数降序排列的同学学号；
select * from score where course_id = 3 and number < 60 order by student_id desc;
41、删除“002”同学的“001”课程的成绩；
select * from score where student_id = 2 and course_id = 1;