作业

5月8号

-- 1、查询所有的课程的名称以及对应的任课老师姓名
SELECT cname, tname from course join teacher on course.teacher_id = teacher.tid;

-- 2、查询学生表中男女生各有多少人
SELECT gender, COUNT(sid) from student GROUP BY gender;

-- 3、查询物理成绩等于100的学生的姓名
SELECT
	sname 
FROM
	student 
WHERE
	sid IN (
	SELECT
		student_id 
	FROM
		score 
	WHERE
		course_id IN ( SELECT cid FROM course WHERE cname = '物理' ) 
	AND num = 100);

-- 4、查询平均成绩大于八十分的同学的姓名和平均成绩
select student.sname, avg(num) from student join score on student.sid = score.student_id
GROUP BY score.student_id
HAVING avg(num) > 80;

-- 5、查询所有学生的学号，姓名，选课数，总成绩
SELECT
    student.sid,
    student.sname,
    t1.course_num,
    t1.total_num
FROM
    student
LEFT JOIN (
    SELECT
        student_id,
        COUNT(course_id) course_num,
        sum(num) total_num
    FROM
        score
    GROUP BY
        student_id
) AS t1 ON student.sid = t1.student_id;


-- 6、 查询姓李老师的个数
SELECT count(tid) FROM teacher WHERE tname LIKE '李%';

-- 7、 查询没有报李平老师课的学生姓名
SELECT
	sname 
FROM
	student 
WHERE
	sid NOT IN (
	SELECT
		student_id 
	FROM
		score 
	WHERE
		course_id IN (
		SELECT
			cid 
		FROM
			course 
		WHERE
		teacher_id IN ( SELECT tid FROM teacher WHERE tname = '李平老师' )));


-- 8、 查询物理课程比生物课程高的学生的学号
SELECT
	t1.student_id 
FROM
	(
	SELECT
		student_id,
		num 
	FROM
		score 
	WHERE
	course_id = ( SELECT cid FROM course WHERE cname = '物理' )) AS t1
	JOIN (
	SELECT
		student_id,
		num 
	FROM
		score 
	WHERE
	course_id = ( SELECT cid FROM course WHERE cname = '生物' )) AS t2 ON t1.student_id = t2.student_id 
WHERE
	t1.num > t2.num;

-- 9、 查询没有同时选修物理课程和体育课程的学生姓名
SELECT
    student.sname
FROM
    student
WHERE
	sid IN (
	SELECT
		student_id 
	FROM
		score 
	WHERE
		course_id IN ( SELECT cid FROM course WHERE cname = '物理' OR cname = '体育' ) 
	GROUP BY
		student_id 
	HAVING
		COUNT( course_id ) = 1 
	);

-- 10、查询挂科超过两门(包括两门)的学生姓名和班级
SELECT
	sname,
	caption 
FROM
	student
	JOIN class ON student.class_id = class.cid 
WHERE
	sid IN (
	SELECT
		student_id 
	FROM
		score 
	WHERE
	num < 60 GROUP BY student_id HAVING COUNT( student_id ) >= 2);

-- 11、查询选修了所有课程的学生姓名
SELECT
    student.sname
FROM
    student
WHERE
    sid IN (
        SELECT
            student_id
        FROM
            score
        GROUP BY
            student_id
        HAVING
            COUNT(course_id) = (SELECT count(cid) FROM course)
    );

-- 12、查询李平老师教的课程的所有成绩记录
SELECT
	* 
FROM
	score 
WHERE
	course_id IN (
	SELECT
		cid 
	FROM
		teacher
		JOIN course ON course.teacher_id = teacher.tid 
	WHERE
	tname = '李平老师');

-- 13、查询全部学生都选修了的课程号和课程名
SELECT
	cid,
	cname 
FROM
	course 
WHERE
	cid IN (
	SELECT
		course_id 
	FROM
		score 
	GROUP BY
		course_id 
	HAVING
	count( student_id ) = ( SELECT count( sid ) FROM student ));

-- 14、查询每门课程被选修的次数
SELECT
	course_id,
	count( student_id ) 
FROM
	score 
GROUP BY
	course_id;

-- 15、查询之选修了一门课程的学生姓名和学号
SELECT
    sid,
    sname
FROM
    student
WHERE
    sid IN (
        SELECT
            student_id
        FROM
            score
        GROUP BY
            student_id
        HAVING
            COUNT(course_id) = 1
    );

-- 16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
select DISTINCT num from score ORDER BY num DESC;

-- 17、查询平均成绩大于85的学生姓名和平均成绩
SELECT
	sname,
	avg( num ) 
FROM
	student
	JOIN score ON student.sid = score.student_id 
GROUP BY
	student_id 
HAVING
	avg( num ) > 85;

-- 18、查询生物成绩不及格的学生姓名和对应生物分数
SELECT
    sname as '姓名',
    num as '生物成绩'
FROM
    score
JOIN course ON score.course_id = course.cid
JOIN student ON score.student_id = student.sid
WHERE course.cname = '生物' AND score.num < 60;

-- 19、查询在所有选修了李平老师课程的学生中，这些课程(李平老师的课程，不是所有课程)平均成绩最高的学生姓名
SELECT
	sname 
FROM
	student 
WHERE
	sid = (
	SELECT
		student_id 
	FROM
		score 
	WHERE
		course_id IN ( SELECT cid FROM course JOIN teacher ON teacher.tid = course.teacher_id WHERE tname = '李平老师' ) 
	GROUP BY
		student_id 
	ORDER BY
		avg( num ) DESC 
	LIMIT 1);

-- 20、查询每门课程成绩最好的前两名学生姓名
select student.sid, student.sname, t4.course_id, t4.first_num, t4.second_num from student join 
(SELECT
    score.student_id as id,
    t3.course_id,
    t3.first_num,
    t3.second_num
FROM
    score
INNER JOIN (
    SELECT
        t1.course_id,
        t1.first_num,
        t2.second_num
    FROM
        (
            SELECT
                course_id,
                max(num) first_num
            FROM
                score
            GROUP BY
                course_id
        ) AS t1
    INNER JOIN (
        SELECT
            score.course_id,
            max(num) second_num
        FROM
            score
        INNER JOIN (
            SELECT
                course_id,
                max(num) first_num
            FROM
                score
            GROUP BY
                course_id
        ) AS t ON score.course_id = t.course_id
        WHERE
            score.num < t.first_num
        GROUP BY
            course_id
    ) AS t2 ON t1.course_id = t2.course_id
) AS t3 ON score.course_id = t3.course_id
WHERE
    score.num >= t3.second_num
AND score.num <= t3.first_num) as t4 on student.sid = t4.id;

-- 21、查询不同课程但成绩相同的学生的学号，课程号，成绩
select score.student_id, score.course_id, score.num, t.course_id, t.num from score join (select student_id, course_id, num from score) as t on t.student_id = score.student_id
WHERE t.num = score.num and t.course_id != score.course_id;

-- 22、查询没学过李平老师课程的学生姓名以及选修的课程名称；
select t.sname, course.cname from 
(SELECT
	sid, sname
FROM
	student 
WHERE
	sid NOT IN (
	SELECT
		student_id 
	FROM
		score 
	WHERE
		course_id IN (
		SELECT
			cid 
		FROM
			course 
		WHERE
		teacher_id IN ( SELECT tid FROM teacher WHERE tname = '李平老师' )))) AS t
LEFT JOIN score ON t.sid = score.student_id
LEFT JOIN course ON course.cid = score.course_id

-- 23、查询所有选修了学号为1的同学选修过的一门或者多门课程的同学学号和姓名；
SELECT
	student_id,
	sname 
FROM
	score
	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;

-- 24、任课最多的老师中学生单科成绩最高的学生姓名

SELECT
	sname 
FROM
	student 
WHERE
	sid IN (
	SELECT
		student_id 
	FROM
		score
		JOIN (
		SELECT
			course_id,
			max( num ) AS n 
		FROM
			(
			SELECT
				student_id,
				course_id,
				num 
			FROM
				score 
			WHERE
				course_id IN (
				SELECT
					cid 
				FROM
					course 
				WHERE
				teacher_id = ( SELECT max( s ) AS id FROM ( SELECT count( teacher_id ) AS s, teacher_id FROM course GROUP BY teacher_id ) AS t ))) AS t 
		GROUP BY
			t.course_id 
		) AS t1 ON t1.course_id = score.course_id 
	WHERE
	score.num = t1.n)

5月6号

完成下列分组查询练习题
1. 查询岗位名以及岗位包含的所有员工名字
select post, group_concat(name) from empp group by post;
2. 查询岗位名以及各岗位内包含的员工个数
select post, count(name) from empp group by post;
3. 查询公司内男员工和女员工的个数
select sex, count(name) as '人数' from empp group by sex;
4. 查询岗位名以及各岗位的平均薪资
select post, avg(salary) from empp GROUP BY post;
5. 查询岗位名以及各岗位的最高薪资
select post, max(salary) from empp GROUP BY post;
6. 查询岗位名以及各岗位的最低薪资
select post, min(salary) from empp GROUP BY post;
7. 查询男员工与男员工的平均薪资，女员工与女员工的平均薪资
select sex, avg(salary) from empp GROUP BY sex;

5月5号
练习：账号信息表，用户组，主机表，主机组

#用户表
create table user(
id int not null unique auto_increment,
username varchar(20) not null,
password varchar(50) not null,
primary key(username,password)
);

#用户组表
create table usergroup(
id int primary key auto_increment,
groupname varchar(20) not null unique
);

#主机表
create table host(
id int primary key auto_increment,
ip char(15) not null unique default '127.0.0.1'
);

#业务线表
create table business(
id int primary key auto_increment,
business varchar(20) not null unique
);

#建关系：user与usergroup

create table user2usergroup(
id int not null unique auto_increment,
user_id int not null,
group_id int not null,
primary key(user_id,group_id),
foreign key(user_id) references user(id),
foreign key(group_id) references usergroup(id)
);

#建关系：host与business
create table host2business(
id int not null unique auto_increment,
host_id int not null,
business_id int not null,
primary key(host_id,business_id),
foreign key(host_id) references host(id),
foreign key(business_id) references business(id)
);

#建关系：user与host
create table user2host(
id int not null unique auto_increment,
user_id int not null,
host_id int not null,
primary key(user_id,host_id),
foreign key(user_id) references user(id),
foreign key(host_id) references host(id)
);

练习:

# 班级表
cid	caption

create table class(
cid int PRIMARY KEY auto_increment,
caption VARCHAR(50) not null
);

# 学生表
sid sname gender class_id

create table student(
sid int PRIMARY key auto_increment,
sname varchar(16) not null,
gender enum('male','female') default 'male',
class_id int,
foreign key(class_id) references class(cid) on update cascade on delete cascade
);

# 老师表
tid	tname

create table teacher(
tid int primary key,
tname varchar(16) not null
);

# 课程表
cid  cname  teacher_id

create table course(
cid int primary key auto_increment,
cname varchar(16) not null,
teacher_id int,
foreign key(teacher_id) references teacher(tid) on update cascade on delete cascade
);

# 成绩表
sid  student_id course_id  number

create table score(
sid int not null unique auto_increment,
student_id int,
course_id int,
number int not null,
primary key(student_id, course_id),
foreign key(student_id) references student(sid),
foreign key(course_id) references course(cid)
);