Apache Pig - Union Operator

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The UNION operator of Pig Latin is used to merge the content of two relations. To perform UNION operation on two relations, their columns and domains must be identical.

Syntax

Given below is the syntax of the UNION operator.

grunt> Relation_name3 = UNION Relation_name1, Relation_name2;

Example

Assume that we have two files namely student_data1.txt and student_data2.txt in the /pig_data/ directory of HDFS as shown below.

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.

And we have loaded these two files into Pig with the relations student1 and student2 as shown below.

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);

Let us now merge the contents of these two relations using the UNION operator as shown below.

grunt> student = UNION student1, student2;

Verification

Verify the relation student using the DUMP operator as shown below.

grunt> Dump student; 

Output

It will display the following output, displaying the contents of the relation student.

(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)