课后作业 day35

#class 添加数据
insert into class (caption) values ('三年二班'),('一年三班'),('三年一班');

#teacher表添加数据
insert into teacher (tname) values ('mom1'),('momo2'),('momo3');

#student 表添加数据
insert into student (sname,gender,class_id) values
	('simple1','female',1),
    ('simple2','female',1),
    ('simple3','male',2);

#创建课程表
create table course(
	cid int auto_increment primary key,
    cname varchar(50) not null default '',
    teacher_id int,
    constraint fk_course_teacher foreign key (teacher_id) references teacher(tid)
)charset utf8;
#course 表添加数据
insert into course (cname,teacher_id) values
	('生物',1),('体育',1),('物理',2);
    
#创建成绩表
create table score(
	sid int auto_increment primary key,
    student_id int,
    course_id int,
    number int not null default 0,
    constraint fk_score_student foreign key (student_id) references student(sid),
    constraint fk_score_course foreign key (course_id) references course(cid)
)charset utf8;
#score 表添数据
insert into score (student_id,course_id,number) values
	(1,1,60),(1,2,59),(2,2,100);

#1.查询所有大于60分的学生的姓名和学号  (DISTINCT: 去重)
select distinct student.sname,student.sid from score left join student on student_id = student.sid where number > 60;

#2.查询每个老师教授的课程数量 和 老师信息
select count(teacher_id) as coursecount,teacher_id,teacher.tname from course left join teacher on teacher_id = teacher.tid group by teacher_id;

#3. 查询学生的信息以及学生所在的班级信息
select sid,sname,gender,class_id,caption from student left join class on class_id = class.cid;

#4、学生中男生的个数和女生的个数
select gender,count('gender') from student group by gender;

#5、获取所有学习'生物'的学生的学号和成绩；姓名
select student_id,number,student.sname from score left join student on student_id = student.sid left join course on course_id = course.cid where course.cname = '生物';

#6、查询平均成绩大于60分的同学的学号和平均成绩； 
select student_id,avg(number) from score group by student_id having avg(number) > 60;

#7、查询姓“李”的老师的个数；
select count(tid) from teacher where tname like '李%';

#8、查询课程成绩小于60分的同学的学号、姓名；
select student_id,student.sname from score left join student on student_id = student.sid where number < 60;

#9. 删除学习“叶平”老师课的SC表记录
delete from score where course_id in (select cid from course left join teacher on teacher_id = teacher.tid where tname = 'mom1');

#10.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(number),min(number) from score group by course_id;

#11.查询每门课程被选修的学生数
select course_id,count(course_id) from score group by course_id;

#12.查询姓“张”的学生名单；
select * from student where sname like '张%';

#13.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) from score group by course_id order by avg(number),course_id desc;

#14.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,student.sname,avg(number) from score left join student on student_id = student.sid group by student_id having avg(number) > 85;

#15.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 student_id,student.sname from score left join student on student_id = student.sid where course_id = 3 and number > 80;

#16.查询各个课程及相应的选修人数
select * from course;

#17.查询“4”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 number < 60 order by number desc;

#18.删除学号为“2”的同学的“1”课程的成绩
delete from score where student_id = 2 and course_id = 2;