hive 数据分析窗口函数之五 GROUPING SETS GROUPING__ID CUBE ROLLUP

所解决的问题：正常情况下只能对一个维度进行group by 聚合，如果多个维度聚合就需要使用 union all 来实现，而grouping 系列函数可以实现一次完成 GROUPING SETS (month,day,(month,day)) 表示聚合了三个 month 一个，day二个（month，day）三个
概述：
GROUPING SETS,GROUPING__ID,CUBE,ROLLUP
这几个分析函数通常用于OLAP中，不能累加，而且需要根据不同维度上钻和下钻的指标统计，比如，分小时、天、月的UV数。
cookie5.txt

2015-03,2015-03-10,cookie1
2015-03,2015-03-10,cookie5
2015-03,2015-03-12,cookie7
2015-04,2015-04-12,cookie3
2015-04,2015-04-13,cookie2
2015-04,2015-04-13,cookie4
2015-04,2015-04-16,cookie4
2015-03,2015-03-10,cookie2
2015-03,2015-03-10,cookie3
2015-04,2015-04-12,cookie5
2015-04,2015-04-13,cookie6
2015-04,2015-04-15,cookie3
2015-04,2015-04-15,cookie2
2015-04,2015-04-16,cookie1

drop table if exists cookie5;
create table cookie5(month string, day string, cookieid string) 
row format delimited fields terminated by ',';
load data local inpath "/home/hadoop/cookie5.txt" into table cookie5;
select * from cookie5;

在一个GROUP BY查询中，根据不同的维度组合进行聚合，等价于将不同维度的GROUP BY结果集进行UNION ALL GROUPING__ID，表示结果属于哪一个分组集合。

玩一玩
把month和day 分别聚合

 select 
  month,
  day,
  count(distinct cookieid) as uv,
  GROUPING__ID
from cookie5 
group by month,day 
grouping sets (month,day) 
order by GROUPING__ID;

等价于

SELECT month,NULL,COUNT(DISTINCT cookieid) AS uv,1 AS GROUPING__ID FROM cookie5 GROUP BY month 
UNION ALL 
SELECT NULL,day,COUNT(DISTINCT cookieid) AS uv,2 AS GROUPING__ID FROM cookie5 GROUP BY day

结果说明

第一列是按照month进行分组

第二列是按照day进行分组

第三列是按照month或day分组是，统计这一组有几个不同的cookieid

第四列grouping_id表示这一组结果属于哪个分组集合，
      根据grouping sets中的分组条件month，day，1是代表month，2是代表day

再比如

SELECT  month, day,
COUNT(DISTINCT cookieid) AS uv,
GROUPING__ID 
FROM cookie5 
GROUP BY month,day 
GROUPING SETS (month,day,(month,day)) 
ORDER BY GROUPING__ID;

等价于

SELECT month,NULL,COUNT(DISTINCT cookieid) AS uv,0 AS GROUPING__ID FROM cookie5 GROUP BY month 
UNION ALL 
SELECT NULL,day,COUNT(DISTINCT cookieid) AS uv,1 AS GROUPING__ID FROM cookie5 GROUP BY day
UNION ALL 
SELECT month,day,COUNT(DISTINCT cookieid) AS uv,2 AS GROUPING__ID FROM cookie5 GROUP BY month,day

GROUPING SETS (month,day,(month,day)) 看出分三个聚合，
第一：month
第二：day
第三：(month,day)

hive 数据分析窗口函数之五 GROUPING SETS GROUPING__ID CUBE ROLLUP

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