11.13日学习记录

46.#查询全部学生都选修的课程的课程号和课程名；
select sc.c,max(course.cname),count(sc.s) from sc join course on(sc.c=course.c)
group by sc.c
having count(sc.score) >(select count(distinct s) from sc)

43.查询每门课程成绩最好的前两名；

SELECT * FROM sc AS a join student on(a.s=student.s)

WHERE 2 > ( SELECT COUNT(*) FROM sc WHERE c = a .c AND score>a .score )
ORDER BY a.score DESC;

40）查询选修“杨艳”老师所授课程的学生中，成绩最高的学生姓名及其成绩；

SELECT student.sname,sc.s,sc.score from sc,student,teacher,course
where sc.score =( select max(a.score) from sc a where a.c=sc.c) and teacher.tname='杨艳' and sc.s = student.s and sc.c=course.c and course.t=teacher.t

1/期间玩手机过程，观看其他网站时间过长，需要控制

2/题目多想想，不要一老看答案，理解完了才算掌握。