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select * from(select animal,age,id,
row_number()over(partition by animal order by age desc) row_num
from zoo)
where row_num <=5;
http://bbs.csdn.net/topics/350001717
oracle取分组的前N条数据
原文地址：http://www.cnblogs.com/oraclesea/p/4195015.html
