7.29数据库(3)笔记

2018-7-29 21:44:40

数据库练习题答案

http://www.cnblogs.com/wupeiqi/p/5748496.html

发现数据库就是记住语句熟练操作,掌握表与表之间的关系就好啦!

和几个朋友打了电话,谈了谈人生,发现,还是我那句话

人的选择不同,自然追求的东西不同!

努力学习,要为以后做打算,加油!!努力!努力!再努力!越努力越幸运!

我命由我不由天!!!!

6.查询没学过'李平老师'老师课的同学的学生姓名(连表操作很多!)

select *from score where num>60;
-- select *from course;
-- select teacher_id,count(cname) from course group by teacher_id
-- select *from course left join teacher on course.teacher_id=teacher.tid;
-- select *from student left join class on student.class_id=class.cid;
-- 临时表
-- select *from (select * from score where num>60)as b;
-- 1.自行创建测试数据
-- 2.查询'生物'课程比'物理'课程成绩搞得所有学生的学号
-- 所有生物成绩
-- SELECT score.sid,score.student_id,course.cname,score.num FROM score left join course on score.course_id=course_id where course.cname='生物';
-- 所有物理成绩
-- SELECT score.sid,score.student_id,course.cname,score.num FROM score left join course on score.course_id=course_id where course.cname='物理';
select A.student_id from
(SELECT score.sid,score.student_id,course.cname,score.num FROM score left join course on score.course_id=course_id where course.cname='物理')as A
INNER JOIN
(SELECT score.sid,score.student_id,course.cname,score.num FROM score left join course on score.course_id=course_id where course.cname='生物')as B
on A.student_id =B.student_id
where A.num >B.num; 
-- 3.查询平均成绩大于60分的同学的学号和平均成绩  显示学生姓名
-- select B.student_id ,student.sname,B.ccc from(select student_id ,avg(num)as ccc from score GROUP BY student_id HAVING avg(num)>60)as B
-- left join B.student_id=student.sid;
-- 4.查询所有同学的学号,姓名,学课数,总成绩
-- select score.student_id,student.sname ,count(student_id),sum(num) from score left join student on score.student_id=student.sid GROUP BY score.student_id;
-- 5.查询李老师个数
-- 6.查询没学过'李平老师'老师课的同学的学生姓名
-- 李平老师任教课程id
-- select course.cid  from course left join teacher on course.teacher_id=teacher.tid where teacher.tname='李平老师;
-- SELECT
--     *
-- FROM
--     (
--         SELECT
--             score.student_id
--         FROM
--             score
--         WHERE
--             course_id NOT IN (
--                 SELECT
--                     course.cid
--                 FROM
--                     course
--                 LEFT JOIN teacher ON course.teacher_id = teacher.tid
--                 WHERE
--                     teacher.tname = '李平老师')
-- )as B
-- left join student on student.sid=B.sid;