hadoop - Hadoop Pig FULL加入

Question

我是PIG的初学者。我的问题是加入后:

ALLDATA1 = join dataA1 by subject FULL, dataT1 by subject;
ALLDATA2 = join ALLDATA1 by dataA1::subject FULL, dataR1 by subject;

我有3栏

ALLDATA1::dataA1::subject, 
ALLDATA1::dataT1::subject, 
dataR1::subject 

我需要所有这些。因为当一个空时，另一个却不空。如何将所有主题放在一列中加入？或在以下情况下热合并此列:当ALLDATA1::dataA1::subject为空时，请使用另一个。

谢谢

Answer 1

获得3列输出后，可以使用三元运算符(是其他常规语言的运算符)来组合3列以生成1。如下所示:

ALLDATA1 = join dataA1 by subject FULL, dataT1 by subject;
ALLDATA2 = join ALLDATA1 by dataA1::subject FULL, dataR1 by subject;

ALLDATA3 = FOREACH ALLDATA2 
               GENERATE
                   ALLDATA1::dataA1::subject IS NOT NULL ?
                       ALLDATA1::dataA1::subject :
                       (ALLDATA1::dataT1::subject IS NOT NULL ? 
                            ALLDATA1::dataT1::subject : 
                            dataR1::subject
                       ) AS subjet;

希望这可以帮助。