Piglatin中的窗口函数（rank over（）等）

Question

是否可以在piglatin中实现Windowing功能？我目前正在使用不支持rank over（）子句的Hive版本。

Answer 1

这可以帮助你：排名是在Pig v.11。(version 12 rank document）和over() was implemented as a piggybank object中实现的。

示例用法：

To do a cumulative sum:

 A = load 'T';
 B = group A by si
 C = foreach B {
     C1 = order A by d;
     generate flatten(Stitch(C1, Over(C1.f, 'sum(float)')));
 }
 D = foreach C generate s, $9;


This is equivalent to the SQL statement

select s, sum(f) over (partition by si order by d) from T;

To find the record 3 ahead of the current record, using a window between the current row and 3 records ahead and a default value of 0.

 A = load 'T';
 B = group A by si;
 C = foreach B {
     C1 = order A by i;
     generate flatten(Stitch(C1, Over(C1.i, 'lead', 0, 3, 3, 0)));
 }
 D = foreach C generate s, $9;


This is equivalent to the SQL statement

select s, lead(i, 3, 0) over (partition by si order by i rows between current row and 3 following) over T;