Apache Pig Union运算符

Pig Latin的 UNION 运算符用于合并两个关系的内容。要对两个关系执行UNION操作,它们的列和域必须相同。

语法

下面给出了 UNION 运算符的语法。

grunt> Relation_name3 = UNION Relation_name1, Relation_name2;

假设在HDFS的 /pig_data/ 目录中有两个文件,即 student_data1.txt  student_data2.txt ,如下所示。

Student_data1.txt

001,Rajiv,Reddy,9848022337,Hyderabad
002,siddarth,Battacharya,9848022338,Kolkata
003,Rajesh,Khanna,9848022339,Delhi
004,Preethi,Agarwal,9848022330,Pune
005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar
006,Archana,Mishra,9848022335,Chennai.
Student_data2.txt

7,Komal,Nayak,9848022334,trivendram.
8,Bharathi,Nambiayar,9848022333,Chennai.
将这两个文件加载到Pig中,通过关系 student1  student2 ,如下所示。

grunt> student1 = LOAD 'hdfs://localhost:9000/pig_data/student_data1.txt' USING PigStorage(',') 
   as (id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray); 
 
grunt> student2 = LOAD 'hdfs://localhost:9000/pig_data/student_data2.txt' USING PigStorage(',') 
   as (id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray);
现在,让我们使用 UNION 运算符合并这两个关系的内容,如下所示。

grunt> student = UNION student1, student2;
验证

使用 DUMP 运算子验证关系student,如下所示。

grunt> Dump student; 

输出

它将显示以下输出,显示关系student的内容。

(1,Rajiv,Reddy,9848022337,Hyderabad) (2,siddarth,Battacharya,9848022338,Kolkata)
(3,Rajesh,Khanna,9848022339,Delhi)
(4,Preethi,Agarwal,9848022330,Pune) 
(5,Trupthi,Mohanthy,9848022336,Bhuwaneshwar)
(6,Archana,Mishra,9848022335,Chennai) 
(7,Komal,Nayak,9848022334,trivendram) 
(8,Bharathi,Nambiayar,9848022333,Chennai)

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