OLAP多维聚合函数
Hive OLAP多维聚合函数是增强版的Group By语句。一般和Group By同时使用，用来进行多维分析。
本文总结Hive三种常用的多维聚合函数:With Cube 任意维度聚合、Grouping Sets 指定维度聚合、With Rollup 层级维度聚合。
测试数据
-- 建表
create table student_scores(
id int,
studentId int,
language int,
math int,
english int,
classId string,
departmentId string
);
-- 写入数据
insert into table student_scores values
(1,111,68,69,90,'class1','department1'),
(2,112,73,80,96,'class1','department1'),
(3,113,90,74,75,'class1','department1'),
(4,114,89,94,93,'class1','department1'),
(5,115,99,93,89,'class1','department1'),
(6,121,96,74,79,'class2','department1'),
(7,122,89,86,85,'class2','department1'),
(8,123,70,78,61,'class2','department1'),
(9,124,76,70,76,'class2','department1'),
(10,211,89,93,60,'class1','department2'),
(11,212,76,83,75,'class1','department2'),
(12,213,71,94,90,'class1','department2'),
(13,214,94,94,66,'class1','department2'),
(14,215,84,82,73,'class1','department2'),
(15,216,85,74,93,'class1','department2'),
(16,221,77,99,61,'class2','department2'),
(17,222,80,78,96,'class2','department2'),
(18,223,79,74,96,'class2','department2'),
(19,224,75,80,78,'class2','department2'),
(20,225,82,85,63,'class2','department2');
With Cube 任意维度聚合
语法:GROUP BY a,b WITH CUBE。
作用:根据Group BY维度的所有可能组合进行聚合。类似于Apache Kylin的Cube多维立方体概念。n个维度会有2的n次方种组合。
select departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores group by departmentid,classid with cube;
结果
departmentid classid summath uv
NULL NULL 1654 20
NULL class1 930 11
NULL class2 724 9
department1 NULL 718 9
department1 class1 410 5
department1 class2 308 4
department2 NULL 936 11
department2 class1 520 6
department2 class2 416 5
等价于union all:
-- 0个维度-没有维度
select null as departmentid,null classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores
union all
-- 1个维度-classid
select null as departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores group by classid
union all
-- 1个维度-departmentid
select departmentid,null as classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores group by departmentid
union all
-- 2个维度-departmentid、classid
select departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores group by departmentid,classid;
Grouping Sets 指定维度聚合
语法:GROUP BY a,b GROUPING SETS (a,b)
作用:根据GROUPING SETS指定维度组合进行聚合。是Cube的一部分。Grouping Sets 分组(Grouping) 集(Sets)，是多个分组的并集。等价于Union ALL单个分组结果。如grouping sets(A,B) 等价于...group by null,B union all ...group by A,null。
select departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores
group by departmentid,classid grouping sets((departmentid,classid),departmentid);
结果:
departmentid classid summath uv
department1 NULL 718 9
department1 class1 410 5
department1 class2 308 4
department2 NULL 936 11
department2 class1 520 6
department2 class2 416 5
等价于union all:
select departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores
group by departmentid,classid
union all
select departmentid,null as classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores
group by departmentid,null;
With Rollup 层级维度聚合
语法:GROUP BY a,b,c WITH ROLLUP
作用:以GROUP BY最左侧的维度为主，从该维度的角度去上卷、下钻。是Cube的一部分。
select departmentid,classid,sum(math) as sumMath,count(distinct studentid) as uv
from student_scores group by departmentid,classid with rollup;