4.2 - MySQL
一、表关系
请创建如下表，并创建相关约束 班级表：class 学生表：student
cid caption grade_id sid sname gender class_id
1 一年一班 1 1 乔丹 女 1
2 二年一班 2 2 艾弗森 女 1
3 三年二班 3 3 科比 男 2 老师表：teacher 课程表：course
tid tname cid cname teacher_id
1 张三 1 生物 1
2 李四 2 体育 1
3 王五 3 物理 2 成绩表：score 年级表：class_grade
sid student_id course_id score gid gname
1 1 1 60 1 一年级
2 1 2 59 2 二年级
3 2 2 99 3 三年级 班级任职表：teach2cls
tcid tid cid
1 1 1
2 1 2
3 2 1
4 3 2 二、操作表
# 题目：
1、自行创建测试数据；
2、查询学生总人数；
3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名；
4、查询每个年级的班级数，取出班级数最多的前三个年级；
5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩；
6、查询每个年级的学生人数；
7、查询每位学生的学号，姓名，选课数，平均成绩；
8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数；
9、查询姓“李”的老师的个数和所带班级数；
10、查询班级数小于5的年级id和年级名；
11、查询班级信息，包括班级id、班级名称、年级、年级级别(12为低年级，34为中年级，56为高年级)，示例结果如下；
班级id 班级名称 年级 年级级别
1 一年一班 一年级 低
12、查询学过“张三”老师2门课以上的同学的学号、姓名；
13、查询教授课程超过2门的老师的id和姓名；
14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名；
15、查询没有带过高年级的老师id和姓名；
16、查询学过“张三”老师所教的所有课的同学的学号、姓名；
17、查询带过超过2个班级的老师的id和姓名；
18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名；
19、查询所带班级数最多的老师id和姓名；
20、查询有课程成绩小于60分的同学的学号、姓名；
21、查询没有学全所有课的同学的学号、姓名；
22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名；
23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名；
24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名；
25、删除学习“张三”老师课的score表记录；
26、向score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“2”课程的同学学号；②插入“2”号课程的平均成绩；
27、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；
28、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；
29、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；
30、课程平均分从高到低显示（显示任课老师）；
31、查询各科成绩前三名的记录(不考虑成绩并列情况)
32、查询每门课程被选修的学生数；
33、查询选修了2门以上课程的全部学生的学号和姓名；
34、查询男生、女生的人数，按倒序排列；
35、查询姓“张”的学生名单；
36、查询同名同姓学生名单，并统计同名人数；
37、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；
38、查询课程名称为“数学”，且分数低于60的学生姓名和分数；
39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名；
40、求选修了课程的学生人数
41、查询选修“王五”老师所授课程的学生中，成绩最高和最低的学生姓名及其成绩；
42、查询各个课程及相应的选修人数；
43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩；
44、查询每门课程成绩最好的前两名学生id和姓名；
45、检索至少选修两门课程的学生学号；
46、查询没有学生选修的课程的课程号和课程名；
47、查询没带过任何班级的老师id和姓名；
48、查询有两门以上课程超过80分的学生id及其平均成绩；
49、检索“3”课程分数小于60，按分数降序排列的同学学号；
50、删除编号为“2”的同学的“1”课程的成绩；
51、查询同时选修了物理课和生物课的学生id和姓名； 建表
create table class_grade(
gid int primary key auto_increment,
gname varchar(16) not null unique
); create table class(
cid int primary key auto_increment,
caption varchar(16) not null,
grade_id int not null,
foreign key(grade_id) references class_grade(gid)
); create table student(
sid int primary key auto_increment,
sname varchar(16) not null,
gender enum('女','男') not null default '女',
class_id int not null,
foreign key(class_id) references class(cid)
); create table teacher(
tid int primary key auto_increment,
tname varchar(16) not null
); create table course(
cid int primary key auto_increment,
cname varchar(16) not null,
teacher_id int not null,
foreign key(teacher_id) references teacher(tid)
); create table score(
sid int not null unique auto_increment,
student_id int not null,
course_id int not null,
score int not null,
primary key(student_id,course_id),
foreign key(student_id) references student(sid)
on delete cascade
on update cascade,
foreign key(course_id) references course(cid)
on delete cascade
on update cascade
); create table teach2cls(
tcid int not null unique auto_increment,
tid int not null,
cid int not null,
primary key(tid,cid),
foreign key(tid) references teacher(tid)
on delete cascade
on update cascade,
foreign key(cid) references class(cid)
on delete cascade
on update cascade
);
建表
准备数据
insert into class_grade(gname) values # 4个年级
('一年级'),
('二年级'),
('三年级'),
('四年级'); insert into class(caption,grade_id) values # 9个班级
('一年一班',1),
('一年二班',1),
('一年三班',1),
('二年一班',2),
('二年二班',2),
('三年一班',3),
('三年二班',3),
('四年一班',4),
('四年二班',4); insert into student(sname,gender,class_id) values # 12个学生
('乔丹','女',1),
('艾弗森','女',1),
('科比','男',2),
('alice','女',2),
('alex','男',3),
('egon','男',4),
('lily','女',5),
('lucy','女',6),
('json','男',6),
('哈妹','女',7),
('霍建华','男',8),
('林心如','女',9); insert into teacher(tname) values # 4个老师
('张三'),
('李四'),
('王五'),
('赵六'); insert into course(cname,teacher_id) values # 9个课程
('生物',1),
('体育',1),
('物理',2),
('化学',3),
('美术',4),
('音乐',2),
('语文',3),
('数学',4),
('地理',2); insert into score(student_id,course_id,score) values # 12个学生，9个课程
(1,1,60),
(1,2,59),
(1,3,58),
(1,4,22),
(1,5,59),
(1,6,60),
(1,7,99),
(1,8,100),
(1,9,88),
(2,1,99),
(2,2,99),
(2,3,89),
(2,4,60),
(2,5,59),
(2,6,33),
(2,7,56),
(2,8,59),
(2,9,60),
(3,1,59),
(3,3,30),
(3,5,28),
(3,7,70),
(3,9,60),
(4,2,59),
(4,4,100),
(4,6,90),
(4,8,80),
(5,1,59),
(5,2,33),
(5,3,12),
(5,4,88),
(6,5,100),
(6,6,60),
(6,7,59),
(6,8,100),
(7,9,20),
(7,1,36),
(7,3,57),
(7,5,60),
(8,2,61),
(8,4,59),
(8,6,62),
(9,8,59),
(9,1,60),
(9,2,61),
(9,3,21),
(10,5,68),
(10,9,99),
(11,1,89),
(11,7,99),
(12,3,100),
(12,8,60); insert into teach2cls(tid,cid) values # 4个老师 9个班级
(1,1),
(1,2),
(1,3),
(1,5),
(2,4),
(2,6),
(2,8),
(2,9),
(2,1),
(2,5),
(3,7),
(3,1),
(3,3),
(3,5),
(3,9),
(4,7),
(4,2),
(4,4),
(4,6),
(4,8),
(4,1);
准备数据
补充数据
insert into score(student_id,course_id,score) values # 12个学生，9个课程
(6,1,60),
(6,3,99),
(10,1,70),
(10,3,88); insert into student(sname,gender,class_id) values # 12个学生
('alice_1','女',1),
('alice_2','女',2); insert into teacher(tname) values # 4个老师
('李杰'); insert into class(caption,grade_id) values # 9个班级
('一年四班',1),
('一年五班',1); insert into class_grade(gname) values # 4个年级
('五年级');
insert into class(caption,grade_id) values # 9个班级
('五年一班',5); insert into course(cname,teacher_id) values # 9个课程
('研究',1); insert into teach2cls(tid,cid) values # 4个老师 9个班级
(1,12),
(2,12); insert into score(student_id,course_id,score) values # 12个学生，9个课程
(1,2,60),
(2,2,59); insert into student(sname,gender,class_id) values # 12个学生
('张一','女',1),
('张二','男',2); insert into student(sname,gender,class_id) values # 12个学生
('张一','女',3),
('张二','男',4); insert into score(student_id,course_id,score) values # 12个学生，9个课程
(7,8,60),
(7,10,60),
(4,10,88),
(6,9,88); insert into score(student_id,course_id,score) values # 12个学生，9个课程
(2,1,60); insert into score(student_id,course_id,score) values # 12个学生，9个课程
(1,1,60),
(2,1,70),
(3,1,80);
补充数据
http://www.cnblogs.com/wupeiqi/articles/5748496.html
答案：
#1、自行创建测试数据；
见table_data.txt #2、查询学生总人数；
select
count(sid) as count_student
from student; #3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名；
select
sid,
sname
from
student
where
sid in (
select
score.student_id
from
score
inner join course on score.course_id = course.cid
where
course.cname in (
'生物',
'物理'
)
and score.score >= 60
group by
score.student_id
having
count(course_id) = 2
); #4、查询每个年级的班级数，取出班级数最多的前三个年级；
select # 没有包含班级数相同得排名前三
class_grade.gname
from
class_grade
inner join (
select
grade_id,
count(cid) as count_cid
from
class
group by
grade_id
order by
count_cid desc
limit 3
) as t1 on class_grade.gid = t1.grade_id; select # 包含了班级数相同得排名前三
gname
from
class_grade
where
gid in (
select
grade_id
from
class
group by
grade_id
having
count(cid) in (
select # 子查询in()里面不能包含limit; This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'
t1.count_cid
from
(
select distinct
count(cid) as count_cid
from
class
group by
grade_id
order by
count_cid desc
limit 3
) as t1
)
); #5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩；
select # 包含了平均成绩相等得情况下，多个学生
student.sid,
student.sname,
t1.avg_score
from
student
inner join (
select
student_id,
avg(score) as avg_score
from
score
group by
student_id
having
avg(score) in (
(
select
avg(score) as max_avg_score
from
score
group by
student_id
order by
avg(score) desc
limit 1
),
(
select
avg(score) as min_avg_score
from
score
group by
student_id
order by
avg(score) asc
limit 1
)
)
) as t1 on student.sid = t1.student_id; #6、查询每个年级的学生人数；
select
t1.grade_id,
count(t1.sid) as count_student
from
(
select
student.sid,
class.grade_id
from
student,
class
where
student.class_id = class.cid
) as t1
group by
t1.grade_id; #7、查询每位学生的学号，姓名，选课数，平均成绩；
select # 包含了没有选课得学生left join
student.sid,
student.sname,
t1.count_course,
t1.avg_score
from
student
left join (
select
student_id,
count(course_id) as count_course,
avg(score) as avg_score
from
score
group by
student_id
) as t1 on student.sid = t1.student_id; #8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数；
select # 包含了成绩最高，最低相等得情况
student.sname,
course.cname,
t1.score
from
(
select
student_id,
course_id,
score
from
score
where
student_id = 2
and score in (
(
select
max(score)
from
score
where
student_id = 2 ),
(
select
min(score)
from
score
where
student_id = 2
)
)
) as t1
inner join student on t1.student_id = student.sid
inner join course on t1.course_id = course.cid; #9、查询姓“李”的老师的个数和所带班级数；
select # 包含了姓"李"的老师没有带班级
teacher.tid,
teacher.tname,
t1.count_cid
from
teacher
left join (
select
tid,
count(cid) as count_cid
from
teach2cls
where
tid in (
select
tid
from
teacher
where
tname like '李%'
)
group by
tid
) as t1 on teacher.tid = t1.tid
where
teacher.tname like '李%'; #10、查询班级数小于5的年级id和年级名；
select
gid,
gname
from
class_grade
where gid in (
select
grade_id
from
class
group by
grade_id
having
count(caption) < 5
); #11、查询班级信息，包括班级id、班级名称、年级、年级级别(12为低年级，34为中年级，56为高年级)，示例结果如下；
班级id 班级名称 年级 年级级别
1 一年一班 一年级 低 select
class.cid,
class.caption,
class_grade.gname,
case when class_grade.gid between 1 and 2 then '低'
when class_grade.gid between 3 and 4 then '中'
when class_grade.gid between 5 and 6 then '高' else 0 end as '年级级别'
from
class,
class_grade
where
class.grade_id = class_grade.gid; #12、查询学过“张三”老师2门课以上的同学的学号、姓名；
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
course.cid
from
teacher,
course
where
teacher.tid = course.teacher_id
and teacher.tname = '张三'
)
group by
student_id
having
count(course_id) > 2
); #13、查询教授课程超过2门的老师的id和姓名；
select
tid,
tname
from
teacher
where
tid in (
select
teacher_id
from
course
group by
teacher_id
having
count(cid) > 2
); #14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名；
select
sid,
sname
from
student
where
sid in (
select distinct
student_id
from
score
where
course_id in (
1,
2
)
); #15、查询没有带过高年级的老师id和姓名；
select
tid,
tname
from
teacher
where
tid not in (
select
tid
from
teach2cls
where
cid in (
select
t1.cid
from
(
select
class.cid,
class.caption,
class_grade.gname,
case when class_grade.gid between 1 and 2 then '低'
when class_grade.gid between 3 and 4 then '中'
when class_grade.gid between 5 and 6 then '高' else 0 end as grade_layer
from
class,
class_grade
where
class.grade_id = class_grade.gid
) as t1
where
t1.grade_layer = '高'
)
); # 另一种方法：
select
tid,
tname
from
teacher
where
tid not in (
select
tid
from
teach2cls
where
cid in (
select
cid
from
class
where
grade_id in (
5,
6
)
)
); #16、查询学过“张三”老师所教的所有课的同学的学号、姓名；
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
cid
from
course
inner join teacher on teacher.tid = course.teacher_id
where teacher.tname = '张三'
)
); #17、查询带过超过2个班级的老师的id和姓名；
select
tid,
tname
from
teacher
where
tid in (
select
tid
from
teach2cls
group by
tid
having
count(cid) > 2
); #18、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名；
select
sid,
sname
from
student
where
sid in (
select
t1.student_id
from
(
select
student_id,
score
from
score
where
course_id = 2
group by
student_id
) as t1,
(
select
student_id,
score
from
score
where
course_id = 1
group by
student_id
) as t2
where
t1.student_id = t2.student_id
and t1.score < t2.score
); #19、查询所带班级数最多的老师id和姓名；
select # 包含了班级数最多相等的情况
tid,
tname
from
teacher
where
tid in (
select
tid
from
teach2cls
group by
tid
having
count(cid) = (
select
count(cid)
from
teach2cls
group by
tid
order by
count(cid) desc
limit 1
)
); #20、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
score < 60
); #21、查询没有学全所有课的同学的学号、姓名；
select
sid,
sname
from
student
where
sid not in (
select
student_id
from
score
group by
student_id
having
count(course_id) = (
select
count(cid)
from
course
)
); #22、查询至少有一门课与学号为“1”的同学所学相同的同学的学号和姓名；
select # 包含了学号为1的同学
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
course_id
from
score
where
student_id = 1
)
group by
student_id
); #23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名；
select # 没有包含学号为1的同学
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
course_id
from
score
where
student_id = 1
)
group by
student_id
)
and sid != 1; #24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名；
select
sid,
sname
from
student
where
sid in (
select
score.student_id
from
score,
(
select
course_id
from
score
where
student_id = 2
) as t1
where
score.course_id = t1.course_id
and score.student_id != 2
group by
score.student_id
having
count(score.course_id) = (
select
count(course_id)
from
score
where
student_id = 2
)
); #25、删除学习“张三”老师课的score表记录；
delete from
score
where
course_id in (
select
course.cid
from
course,
teacher
where
course.teacher_id = teacher.tid
and teacher.tname = '张三'
) #26、向score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“2”课程的同学学号；②插入“2”号课程的平均成绩；
insert into score(student_id,course_id,score)
select
t1.sid,
2,
t2.avg_score
from
(
select
sid
from
student
where
sid not in (
select
student_id
from
score
where
course_id = 2
)
) as t1,
(
select
avg(score) as avg_score
from
score
where
course_id = 2
) as t2; #27、按平均成绩从低到高显示所有学生的“语文”、“数学”、“音乐”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,音乐,有效课程数,有效平均分； # ****
select
sc.student_id,
(select score.score from score left join course on score.course_id = course.cid where course.cname = '语文' and score.student_id = sc.student_id) as yw,
(select score.score from score left join course on score.course_id = course.cid where course.cname = '数学' and score.student_id = sc.student_id) as sx,
(select score.score from score left join course on score.course_id = course.cid where course.cname = '音乐' and score.student_id = sc.student_id) as yy,
count(sc.course_id),
avg(sc.score)
from
score as sc
group by
sc.student_id
order by
avg(sc.score) asc; #28、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.cid,
max(score.score) as max_score,
min(score.score) as min_score
from
course
left join score on course.cid = score.course_id
group by
score.course_id; #29、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
course_id,
avg(score) as avg_score,
sum(case when score.score > 60 then 1 else 0 end) / count(1) * 100 as percent
from
score
group by
course_id
order by
avg(score) asc,
percent desc; #30、课程平均分从高到低显示（显示任课老师）；
select
t1.course_id,
t1.avg_score,
teacher.tname
from
course,
teacher,
(
select
course_id,
avg(score) as avg_score
from
score
group by
course_id
order by
avg_score desc
) as t1
where
course.cid = t1.course_id
and course.teacher_id = teacher.tid
order by
t1.avg_score desc; #31、查询各科成绩前三名的记录(不考虑成绩并列情况) # 和44题相似！！
select
score.sid,
score.student_id,
score.course_id,
score.score,
t1.first_score,
t1.second_score,
t1.third_score
from
score
inner join (
select
s1.sid,
(select score from score as s2 where s1.course_id = s2.course_id order by score desc limit 0,1) as first_score,
(select score from score as s3 where s1.course_id = s3.course_id order by score desc limit 1,1) as second_score,
(select score from score as s4 where s1.course_id = s4.course_id order by score desc limit 2,1) as third_score
from
score as s1
) as t1 on score.sid = t1.sid
where
score.score in (
t1.first_score,
t1.second_score,
t1.third_score
); #32、查询每门课程被选修的学生数；
select # 包含了没有被选修的课程显示0
course.cid,
ifnull(t1.count_students,0) as count_student
from
course
left join (
select
course_id,
count(student_id) as count_students
from
score
group by
course_id
) as t1 on course.cid = t1.course_id; #33、查询选修了2门以上课程的全部学生的学号和姓名；
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
group by
student_id
having
count(course_id) > 2
); #34、查询男生、女生的人数，按倒序排列；
select
gender,
count(sid) as count_student
from
student
group by
gender
order by
count_student desc; #35、查询姓“张”的学生名单；
select
student.sid,
student.sname,
student.gender,
class.caption
from
student
inner join class on student.class_id = class.cid
where
student.sname like '张%'; #36、查询同名同姓学生名单，并统计同名人数；
select
sname,
count(sname) as count_sname
from
student
group by
sname
having
count(sname) > 1; #37、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(score) as avg_score
from
score
group by
course_id
order by
avg_score,
course_id desc; #38、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,
t1.score
from
student
inner join (
select
score.student_id,
score.score
from
score
inner join course on score.course_id = course.cid
where
course.cname = '数学'
and score.score < 60
) as t1 on student.sid = t1.student_id; #39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名；
select
sid,
sname
from
student
where sid in (
select
student_id
from
score
where
course_id = 3
and score > 80
); #40、求选修了课程的学生人数
select
course_id,
count(student_id) as count_student
from
score
group by
course_id; #41、查询选修“王五”老师所授课程的学生中，成绩最高和最低的学生姓名及其成绩；
select # 教的课可能包含多门，按课程id来分的！包含了最高，最低成绩相等的情况
student.sname,
t2.course_id,
t2.score,
t2.max_score,
t2.min_score
from
student
inner join (
select
score.student_id,
score.course_id,
score.score,
t1.max_score,
t1.min_score
from
score,
(
select
course_id,
max(score) as max_score ,
min(score) as min_score
from
score
where
course_id in (
select
cid
from
course
inner join teacher on course.teacher_id = teacher.tid
where
teacher.tname = '王五'
)
group by
course_id
) as t1
where
score.course_id = t1.course_id
and score.score in (
max_score,
min_score
)
) as t2 on student.sid = t2.student_id; #42、查询各个课程及相应的选修人数；
select # 包含了没有被选修的课程显示0
course.cname,
ifnull(t1.count_student,0) as count_student
from
course
left join (
select
course_id,
count(student_id) as count_student
from
score
group by
course_id
) as t1 on course.cid = t1.course_id; #43、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 # 不同的学生之间，成绩相同 这里有问题！！
s1.student_id,
s2.student_id,
s1.course_id as s1_course_id,
s2.course_id as s2_course_id,
s1.score,
s2.score
from
score as s1,
score as s2
where
s1.course_id != s2.course_id
and s1.score = s2.score; select distinct # 同一个学生，成绩相同
s1.student_id,
s2.student_id,
s1.course_id as s1_course_id,
s2.course_id as s2_course_id,
s1.score,
s2.score
from
score as s1,
score as s2
where
s1.student_id = s2.student_id
and s1.course_id != s2.course_id
and s1.score = s2.score; #44、查询每门课程成绩最好的前两名学生id和姓名； #??? 这里有个问题,成绩相同的学生，会都录入！！
select
student.sid,
student.sname,
t2.course_id,
t2.score,
t2.first_score,
t2.second_score
from
student
inner join ( # 这里会出现成绩相同的情况，录入了超过了两名的学生！！
select
score.student_id,
score.course_id,
score.score,
t1.first_score,
t1.second_score
from
score
inner join (
select
s1.sid,
(select s2.score from score as s2 where s1.course_id = s2.course_id order by s2.score desc limit 0,1) as first_score,
(select s3.score from score as s3 where s1.course_id = s3.course_id order by s3.score desc limit 1,1) as second_score
from
score as s1
) as t1 on score.sid = t1.sid
where
score.score in ( # ？？在这，会超过两个！！
t1.first_score,
t1.second_score
)
) as t2 on student.sid = t2.student_id; **************************************************************
# 这个有排名 包括了成绩相同的！
select c.sname, d.cname, a.score
from score a
inner join (
select course_id, score, rank
from (
select a.course_id, a.score, count(*) as rank
from (select course_id, score
from score
group by course_id, score
order by course_id, score desc) a
inner join (select course_id, score
from score
group by course_id, score
order by course_id, score desc) b
on a.course_id = b.course_id
and a.score <= b.score
group by course_id, score
) t1
where rank in (1, 2)
order by course_id, rank
) b
on a.course_id = b.course_id
and a.score = b.score
inner join student c
on a.student_id = c.sid
inner join course d
on a.course_id = d.cid; ************************************************************** #45、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; #46、查询没有学生选修的课程的课程号和课程名；
select
cid,
cname
from
course
where
cid not in (
select
course_id
from
score
group by
course_id
); #47、查询没带过任何班级的老师id和姓名；
select
tid,
tname
from
teacher
where
tid not in (
select
tid
from
teach2cls
group by
tid
); #48、查询有两门以上课程超过80分的学生id及其平均成绩；
select
student_id,
avg(score) as avg_score
from
score
where
student_id in (
select
student_id
from
score
where
score > 80
group by
student_id
having
count(course_id) > 2
)
group by
student_id; #49、检索“3”课程分数小于60，按分数降序排列的同学学号；
select
student_id,
score
from
score
where
course_id = 3
and score < 60
order by
score desc; #50、删除编号为“2”的同学的“1”课程的成绩；
delete from # 需要在包一层select(),否则 You can't specify target table 'score' for update in FROM clause
score
where
sid = (
select
t1.sid
from
(
select
sid
from
score
where
student_id = 2
and course_id = 1
) as t1
); #51、查询同时选修了物理课和生物课的学生id和姓名；
select
sid,
sname
from
student
where
sid in (
select
student_id
from
score
where
course_id in (
select
cid
from
course
where
course.cname in (
'物理',
'生物'
)
)
group by
student_id
having
count(course_id) = 2
);
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