mysql作业
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 left 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 #子查询的方式 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 ); #连表的方式 select sname from student inner join ( select student_id from score where course_id = (select cid from course where cname='物理') and num=100 ) as a on a.student_id=student.sid ; 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,t1.平均成绩 from student inner join (select student_id,avg(num) 平均成绩 from score group by student_id having avg(num) > 80) as t1 on student.sid=t1.student_id; 5、查询所有学生的学号,姓名,选课数,总成绩 select student.sid,sname 学生名,选课数,总成绩 from student left join (select student_id,count(course_id) 选课数,sum(num) 总成绩 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 distinct 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 inner join course on score.course_id=course.cid where course.cname='物理') as t1 inner join (select student_id,num from score inner join course on score.course_id=course.cid where course.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 sname from student where sid in ( select student_id from score inner join cour on course.cname in ('物理','体育') and course.cid=score.course_id group by student_id having count(course_id) !=2 ); 10、查询挂科超过两门(包括两门)的学生姓名和班级名字 select t2.sname,class.caption from (select sname,class_id from student inner join ( select student_id from score where num < 60 group by student_id having count(course_id) >=2 ) as t1 on student.sid=t1.student_id) as t2 inner join class on class.cid = t2.class_id ; 11 、查询选修了所有课程的学生姓名 select sname from student inner join ( select student_id from score group by student_id having count(course_id) = (select count(cid) from course) ) t1 on t1.student_id = student.sid ; 12、查询李平老师教的课程的所有成绩记录 select student_id,course_id,num from score inner join ( select cid from course inner join teacher on teacher.tname='李平老师' and teacher.tid=course.teacher_id ) as t1 on t1.cid=score.course_id ; 13、查询全部学生都选修了的课程号和课程名 select course.cid,course.cname from course inner join ( select course_id from score group by course_id having count(student_id) = (select count(sid) from student) ) t1 on t1.course_id=course.cid ; 14、查询每门课程被选修的次数 select course.cname,选修人数 from course inner join ( select course_id,count(student_id) as 选修人数 from score group by course_id ) as t1 on t1.course_id=course.cid ; 15、查询之选修了一门课程的学生姓名和学号 select sid,sname from student inner join ( select student_id from score group by student_id having count(course_id)=1 ) t1 on t1.student_id = student.sid ; 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 student.sname,avg_num from student inner join ( select student_id,avg(num) as avg_num from score group by student_id having avg(num) > 85 ) t1 on student.sid=t1.student_id ; 18、查询生物成绩不及格的学生姓名和对应生物分数 select student.sname,t1.num from student inner join ( select student_id,num from score where course_id=(select cid from course where cname='生物') and num < 60 ) t1 on t1.student_id=student.sid ; 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 inner join teacher on teacher.tname='李平老师' and course.teacher_id=teacher.tid ) group by student_id order by avg(num) desc limit 1 );