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What is ORDER BY operator in Apache Pig ?

  • The ORDER BY operator is used to display the contents of a relation in a sorted order based on one or more fields. (or) ORDER BY operator is used to sort the data in ascending or descending order, based on one or more columns.
  • Some data sort the results in an ascending order by default.
  • ORDER BY instruction:
    • Sorts relations by a specific criteria
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    Syntax

    grunt> Relation_name2 = ORDER Relation_name1 BY (ASC|DESC);
    

    Example

    • Ensure that we have a file named wikitechy_employee_details.txt in the HDFS directory /pig_data/ as given below.

    Wikitechy_employee_details.txt

    111,Anu,Shankar,23,9876543210,Chennai
    112,Barvathi,Nambiayar,24,9876543211,Chennai
    113,Kajal,Nayak,24,9876543212,Trivendram
    114,Preethi,Antony,21,9876543213,Pune
    115,Raj,Gopal,21,9876543214,Hyderabad
    116,Yashika,Kannan,22,9876543215,Delhi
    117,siddu,Narayanan,22,9876543216,Kolkata
    118,Timple,Mohanthy,23,9876543217,Bhuwaneshwar
    
    • And we have loaded this file into Pig with the relation name wikitechy_student_details as shown below.
    grunt> student_details = LOAD 'hdfs://localhost:9000/pig_data/student_details.txt' USING PigStorage(',')
       as (id:int, firstname:chararray, lastname:chararray,age:int, phone:chararray, city:chararray);
    
    • Here sort the relation in a descending order based on the age of the employee and store it into another relation named order_by_data using the ORDER BY operator as given below.
    grunt> order_by_data = ORDER wikitechy_employee_details BY age DESC;
    

    Verification:

    • Now verify the relation order_by_data using the DUMP operator as given below.
    grunt> Dump order_by_data; 
    

    Output

    • The following output, display the contents of the relation order_by_data.
    113,Kajal,Nayak,24,9876543212,Trivendram
    112,Barvathi,Nambiayar,24,9876543211,Chennai
    118,Timple,Mohanthy,23,9876543217,Bhuwaneshwar
    
    111,Anu,Shankar,23,9876543210,Chennai
    117,siddu,Narayanan,22,9876543216,Kolkata
    116,Yashika,Kannan,22,9876543215,Delhi
    115,Raj,Gopal,21,9876543214,Hyderabad
    114,Preethi,Antony,21,9876543213,Pune
    

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