豬加入空值

Question

雖然實施解決方案提供的How to optimize a group by statement in PIG latin?我發現有一個空列的所有行都被刪除，這是Pig中的預期行爲。我想知道下面的代碼是否可以工作？

A = B join by (Bcol1 is null?'UNK',Bcol2 is null?'UNK',Bcol2 is null?999), 
C join by (Ccol1 is null?'UNK',Ccol2 is null?'UNK',Ccol2 is null?999) 

我得到一些解析錯誤。

Answer 1

PIG是一種數據流腳本語言，並增加了額外的FOREACH GENERATE，它修復了null，不會導致額外的map reduce任務。

B = foreach B generate ....., (Bcol1 is null) ? 'UNK' : Bcol1 as Bcol1, (Bcol2 is null) ? 'UNK' : Bcol2 as Bcol2, (Bcol3 is null) ? 999 : Bcol3; 
C = foreach C generate ....., (Ccol1 is null) ? 'UNK' : Ccol1 as Ccol1, (Ccol2 is null) ? 'UNK' : Ccol2 as Ccol2, (Ccol3 is null) ? 999 : Ccol3; 
A = join B by (Bcol1, Bcol2, Bcol3), C by (Ccol1, Ccol2, Ccol3);