重修课程day45（mysql之练习题二）

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 inner 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 = (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

方法1：
SELECT student.sname,t1.avg_num from student inner join
(SELECT student_id,AVG(num) avg_num from score GROUP BY student_id
HAVING avg(num) > 80) as t1
on student.sid = t1.student_id;


方法2：
select * from student where sid in (
	select student_id from score group by 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 inner 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
方法1：
SELECT COUNT(1) from teacher where tname like ‘李%‘;


方法2：
select count(t1) from (
	select tname t1 from teacher where tname LIKE ‘李%‘
)as t



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 = (
						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
inner 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
方法1：
SELECT sname from student where sid in (
SELECT student_id from score LEFT JOIN course
on score.course_id = course.cid
WHERE course.cname in (‘物理‘,‘体育‘)
GROUP BY student_id
HAVING count(sid) < 2
);


方法2：
select sname from student where sid not in (
SELECT s1.student_id from (
select student_id from score where course_id =(
SELECT cid from course where cname =‘体育‘)) s1
INNER JOIN (
select student_id from score where course_id =(
SELECT cid from course where cname =‘物理‘)) s2
 on s1.student_id=s2.student_id);


10、查询挂科超过两门(包括两门)的学生姓名和班级
方法1：：
SELECT sname,caption from student LEFT JOIN class
on student.class_id = class.cid
where student.sid in (
SELECT student_id from score where num < 60 GROUP BY student_id
HAVING COUNT(course_id) >= 2
)
;


方法2：
 select s.sname,class.caption from class INNER JOIN
	(select * from student where sid in (
		select student_id from score GROUP BY student_id
		having student_id>=2)) s
			on s.class_id=class.cid;


11 、查询选修了所有课程的学生姓名
select sname from student where sid in (
select student_id from score GROUP BY student_id
having count(sid)=(
select count(cid) from course))


12、查询李平老师教的课程的所有成绩记录
方法1：
SELECT * from score where course_id in (
SELECT cid from course inner JOIN teacher
on course.teacher_id = teacher.tid
WHERE tname = ‘李平老师‘
);


方法2：
select num from score WHERE course_id in (
select cid from course where teacher_id=(
select tid from teacher 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 ss.s1,ss.s2,course.cid,course.cname from
(select student.sid s1,student.sname s2,score.course_id s3
	from student INNER JOIN score
 	on student.sid=score.student_id ) ss
 INNER JOIN course
 on ss.s3=course.cid;

14、查询每门课程被选修的次数
方法1：
SELECT course.cname,t1.count_student FROM course
INNER JOIN
(
SELECT course_id,count(student_id) count_student from score GROUP BY course_id
) as t1
ON course.cid = t1.course_id;


方法2：
select course.cname,COUNT(score.sid)
from course INNER JOIN score
	on course.cid=score.course_id
 		group by score.course_id;

15、查询只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(sid)=1);


16、查询所有学生考出的总成绩并按从高到低排序（成绩去重）
方法1：
SELECT  DISTINCT sum(num) sum_num from score group by student_id
ORDER BY sum_num desc;

方法2：
select  student.sname,avg(score.num) avg_num from
	student INNER JOIN score on student.sid=score.student_id
	GROUP BY student_id ORDER BY avg_num desc;


17、查询平均成绩大于85的学生姓名和平均成绩
方法1：
SELECT student.sname,t1.avg_num from student inner join
(
SELECT student_id,avg(num) avg_num from score GROUP BY student_id having avg(num) > 85
) as t1
on student.sid = t1.student_id;


方法2：
 select student.sname,avg(score.num) from student INNER JOIN score
	on student.sid=score.student_id
		GROUP BY score.student_id
		having avg(score.num)>85;


18、查询生物成绩不及格的学生姓名和对应生物分数
方法1：
SELECT sname,t1.num from student
INNER JOIN
(
SELECT student_id,num from score LEFT JOIN course
on score.course_id = course.cid
where course.cname = ‘生物‘ and score.num < 60
) as t1
on student.sid = t1.student_id;



方法2：
select student.sname,ss.num from student INNER JOIN(
select * from score where course_id=(
select cid from course where cname=‘生物‘) and num<60) ss
on ss.student_id=student.class_id;



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 in(
 select student_id from score where course_id in(
select cid from course where teacher_id=(
select tid from teacher where tname=‘李平老师‘))
 GROUP BY student_id
 HAVING avg(num)=(
 select  avg(num) from score where course_id in(
 select cid from course where teacher_id=(
 select tid from teacher 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 * from score ORDER BY course_id,num desc;

#取得课程编号与第一高的成绩:course_id,first_num
SELECT course_id,max(num) first_num from score GROUP BY course_id;


#取得课程编号与第二高的成绩:course_id,second_num
SELECT score.course_id,max(num) second_num from score LEFT JOIN (
SELECT course_id,max(num) first_num from score GROUP BY course_id

) as t1
on score.course_id = t1.course_id
where score.num < t1.first_num
GROUP BY score.course_id
;

#链表得到一张新表，新表包含课程编号与这门课程前两名的成绩分数

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 LEFT JOIN (
SELECT course_id,max(num) first_num from score GROUP BY course_id

) as t1
on score.course_id = t1.course_id
where score.num < t1.first_num
GROUP BY score.course_id) as t2

on t1.course_id = t2.course_id;


#取前两名学生的编号

SELECT score.course_id,score.student_id from score LEFT 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 LEFT JOIN (
SELECT course_id,max(num) first_num from score GROUP BY course_id

) as t1
on score.course_id = t1.course_id
where score.num < t1.first_num
GROUP BY score.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
;

SELECT t4.course_id,student.sname from student inner join
(
SELECT score.course_id,score.student_id from score LEFT 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 LEFT JOIN (
SELECT course_id,max(num) first_num from score GROUP BY course_id

) as t1
on score.course_id = t1.course_id
where score.num < t1.first_num
GROUP BY score.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.student_id
ORDER BY t4.course_id
;



select student.sname,t.course_id,t.num from student INNER JOIN
(
select
			s1.student_id,s1.course_id,s1.num,
			(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 student.sid =  t.student_id
where t.num in (t.first_num,t.second_num)
ORDER BY t.course_id
;


SELECT sid from score as s1 ;