2丶查询‘生物’课程比‘物理’课程成绩高的所有学生的学号
思路：
获取所有有生物课成的人（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
然后在进行筛选
select A.studeny_id,sw,ty from
(select student_id,num as sw from score left join coure.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 = '物理') as B
3丶查询平均成绩大于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丶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),stident.sname
from
score left join sudent on score.student_id = student.sid
group by score.student_id
5丶查询姓“李”的老师的个数：
1, select count(tid) from teacher where tname like '李%'
2, select count(1) from (select tid from teacher where tname like '李%') as B
6丶查询没学过‘叶平’老师课的同学的学号,姓名：
思路：
先查到‘李平老师’所教的所有课的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丶查询学过‘001’并且也学过编号‘002’课程的同学的学号,姓名：
思路：
先查到即选择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 couse_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丶查询学过‘叶平’老师所教的所有课的学号,姓名：
同上,支部过奖001和002变成了 in （叶平老师的所有课）
9丶查询课程编号'002'的成绩比课程编号‘001’课程低的所有同学的学号,姓名：
同第一题
10丶查询所有课程成绩小于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丶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,获取没一个学生选课数量
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丶查询只收有一门课与学号为‘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
获取课程在其中的素偶有人一级所有课程
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丶查询只少学过学号为‘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 == > 其他人可以选择的更多
select student_id,sname,count(course_id)
from score left join student on score 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丶查询和'002'号的同学学习的课程完全相同的其他同学学号的姓名:
个数相同
002学过的也相同
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丶删除学习‘叶平’老师课的score表记录
delete from score where course_id in (
select cid from course left join tecaher on course.teacher_id = teacher.tid where teacher.name = '叶平'
)
16丶向sc表中插入一些记录,这些记录要求符合以下条件:没有上过编号'002'课程的同学学号:插入‘002’号课程的平均成绩:
思路:
由于insert 支持
insert 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丶按平均成绩从低到高显示所有学生的‘语文’，‘数学’，‘英语’三门课程成绩,按如下形式显示:学生ID,语文,数学,英语,有效课程，有效平均分：
select sc.student_id,
(select num from score left join course on score.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 w,
(select num from 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丶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丶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 where ... thed
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丶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
