Apache Pig Union operator

Pig Latin's UNION operator is used to merge the contents of two relationships. /b10> To perform UNION operations on two relationships, their columns and domains must be the same.

Grammar

The syntax of the UNION operator is given below.

grunt> Relation_name3 = UNION Relation_name1, Relation_name2;

Cases

Suppose you have two files in the /pig_data/directory of HDFS, student_data1.txt and student_data2.txt, 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.

Load the two files into pig, via relationships 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);

Now, let's use the UNION operation to match the contents of both relationships, as shown below.

grunt> student = UNION student1, student2;

Verify

Use the DUMP operation sub-validation relationship student, as shown below.

grunt> Dump student; 

Output

It displays the following output, showing the contents of the relationship 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)