create table student ( sid varchar2(10), --学号 sname varchar2(10), --姓名 classid varchar2(10), --班级号 score int --分数);
问题一： 班级中平均分最高的 班级号 以及 分数；
insert into student values('001','z001','1',80);insert into student values('002','z001','1',90);insert into student values('003','z001','1',70);insert into student values('004','z001','1',90);insert into student values('005','z001','1',80);insert into student values('006','z001','1',70);insert into student values('007','z001','2',60);insert into student values('008','z001','2',70);insert into student values('009','z001','2',50);insert into student values('010','z001','2',70);insert into student values('011','z001','2',60);insert into student values('012','z001','2',50);--求解sql： SELECT * FROM (SELECT CLASSID,AVG(score) score_ FROM STUDENT GROUP BY CLASSID ORDER BY score_ DESC) WHERE ROWNUM=1 ;
问题二： 求每个班级第二名的学生的 学号 和 分数 （如果并列第二，全部求出）
原始数据：
执行如下sql：
select s.* from (select t.* , dense_rank() over(partition by classid order by score) as cn from student t ) s where s.cn = 2;
分析以上sql：
select t.* , dense_rank() over(partition by classid order by score) as cn from student t
以上sql的执行结果：
以下是 row_number() 和 dense_rank的区别： 区别在于最后一行 cn 上
select t.* , row_number() over(partition by classid order by score) as cn from student t
rank() 的用法：
select t.* , RANK() over(partition by classid order by score) as cn from student t
