问题导读： 1.ntile作用是什么？ 2.按照pv降序排列，生成分组内每天的pv名次可使用哪个窗口函数？ 3.rank 和 dense_rank作用是什么？ 接上篇：hive分析窗口函数（一）sum,avg,min,max 本文中介绍前几个序列函数，ntile,row_number,rank,dense_rank，下面会一
问题导读：
1.ntile作用是什么？
2.按照pv降序排列，生成分组内每天的pv名次可使用哪个窗口函数？
3.rank 和 dense_rank作用是什么？
接上篇：hive分析窗口函数（一）sum,avg,min,max
本文中介绍前几个序列函数，ntile,row_number,rank,dense_rank，下面会一一解释各自的用途。
hive版本为 apache-hive-0.13.1
注意： 序列函数不支持window子句。（什么是window子句，hive分析窗口函数（一）sum,avg,min,max) 
数据准备：
cookie1,2015-04-10,1 cookie1,2015-04-11,5 cookie1,2015-04-12,7 cookie1,2015-04-13,3 cookie1,2015-04-14,2 cookie1,2015-04-15,4 cookie1,2015-04-16,4 cookie2,2015-04-10,2 cookie2,2015-04-11,3 cookie2,2015-04-12,5 cookie2,2015-04-13,6 cookie2,2015-04-14,3 cookie2,2015-04-15,9 cookie2,2015-04-16,7 create external table lxw1234 ( cookieid string, createtime string, --day pv int ) row format delimited fields terminated by ',' stored as textfile location '/tmp/lxw11/'; desc lxw1234; cookieid string createtime string pv int hive> select * from lxw1234; ok cookie1 2015-04-10 1 cookie1 2015-04-11 5 cookie1 2015-04-12 7 cookie1 2015-04-13 3 cookie1 2015-04-14 2 cookie1 2015-04-15 4 cookie1 2015-04-16 4 cookie2 2015-04-10 2 cookie2 2015-04-11 3 cookie2 2015-04-12 5 cookie2 2015-04-13 6 cookie2 2015-04-14 3 cookie2 2015-04-15 9 cookie2 2015-04-16 7
ntile
ntile(n)，用于将分组数据按照顺序切分成n片，返回当前切片值
ntile不支持rows between，比如 ntile(2) over(partition by cookieid order by createtime rows between 3 preceding and current row)
如果切片不均匀，默认增加第一个切片的分布
select cookieid, createtime, pv, ntile(2) over(partition by cookieid order by createtime) as rn1, --分组内将数据分成2片 ntile(3) over(partition by cookieid order by createtime) as rn2, --分组内将数据分成3片 ntile(4) over(order by createtime) as rn3 --将所有数据分成4片 from lxw1234 order by cookieid,createtime; cookieid day pv rn1 rn2 rn3 ------------------------------------------------- cookie1 2015-04-10 1 1 1 1 cookie1 2015-04-11 5 1 1 1 cookie1 2015-04-12 7 1 1 2 cookie1 2015-04-13 3 1 2 2 cookie1 2015-04-14 2 2 2 3 cookie1 2015-04-15 4 2 3 3 cookie1 2015-04-16 4 2 3 4 cookie2 2015-04-10 2 1 1 1 cookie2 2015-04-11 3 1 1 1 cookie2 2015-04-12 5 1 1 2 cookie2 2015-04-13 6 1 2 2 cookie2 2015-04-14 3 2 2 3 cookie2 2015-04-15 9 2 3 4 cookie2 2015-04-16 7 2 3 4
比如，统计一个cookie，pv数最多的前1/3的天
select cookieid, createtime, pv, ntile(3) over(partition by cookieid order by pv desc) as rn from lxw1234; --rn = 1 的记录，就是我们想要的结果 cookieid day pv rn ---------------------------------- cookie1 2015-04-12 7 1 cookie1 2015-04-11 5 1 cookie1 2015-04-15 4 1 cookie1 2015-04-16 4 2 cookie1 2015-04-13 3 2 cookie1 2015-04-14 2 3 cookie1 2015-04-10 1 3 cookie2 2015-04-15 9 1 cookie2 2015-04-16 7 1 cookie2 2015-04-13 6 1 cookie2 2015-04-12 5 2 cookie2 2015-04-14 3 2 cookie2 2015-04-11 3 3 cookie2 2015-04-10 2 3
row_number() –从1开始，按照顺序，生成分组内记录的序列
–比如，按照pv降序排列，生成分组内每天的pv名次
row_number() 的应用场景非常多，再比如，获取分组内排序第一的记录;获取一个session中的第一条refer等。
select cookieid, createtime, pv, row_number() over(partition by cookieid order by pv desc) as rn from lxw1234; cookieid day pv rn ------------------------------------------- cookie1 2015-04-12 7 1 cookie1 2015-04-11 5 2 cookie1 2015-04-15 4 3 cookie1 2015-04-16 4 4 cookie1 2015-04-13 3 5 cookie1 2015-04-14 2 6 cookie1 2015-04-10 1 7 cookie2 2015-04-15 9 1 cookie2 2015-04-16 7 2 cookie2 2015-04-13 6 3 cookie2 2015-04-12 5 4 cookie2 2015-04-14 3 5 cookie2 2015-04-11 3 6 cookie2 2015-04-10 2 7
rank 和 dense_rank
—rank() 生成数据项在分组中的排名，排名相等会在名次中留下空位
—dense_rank() 生成数据项在分组中的排名，排名相等会在名次中不会留下空位
select cookieid, createtime, pv, rank() over(partition by cookieid order by pv desc) as rn1, dense_rank() over(partition by cookieid order by pv desc) as rn2, row_number() over(partition by cookieid order by pv desc) as rn3 from lxw1234 where cookieid = 'cookie1'; cookieid day pv rn1 rn2 rn3 -------------------------------------------------- cookie1 2015-04-12 7 1 1 1 cookie1 2015-04-11 5 2 2 2 cookie1 2015-04-15 4 3 3 3 cookie1 2015-04-16 4 3 3 4 cookie1 2015-04-13 3 5 4 5 cookie1 2015-04-14 2 6 5 6 cookie1 2015-04-10 1 7 6 7 rn1: 15号和16号并列第3, 13号排第5 rn2: 15号和16号并列第3, 13号排第4 rn3: 如果相等，则按记录值排序，生成唯一的次序，如果所有记录值都相等，或许会随机排吧。