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What is describe operator?

  • The describe operator is used to view the schema of a relation.
  • It Returns the schema of a relation.
  • DESCRIBE instruction:
    • Prints the schema of the relation at standard output
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    Syntax:

    • The syntax of the describe operator is as follows −
    grunt> Describe Relation_name
    

    Usage:

    • Use the DESCRIBE operator to view the schema of a relation.
    • You can view outer relations as well as relations defined in a nested FOREACH statement.

    Example:

    • Assume we have a file student_data.txt in HDFS with the following content.
    001, Aadhira,Arushi,9848022337, Delhi
    002, Mahi,Champa,9848022338, Chennai
    003, Avantika,charu,9848022339, Pune
    004, Samaira,Hansa,9848022330, Kolkata
    005, Abhinav,Akaash,9848022336,Bhuwaneshwar
    006, Amarjeet,Aksat,9848022335, Hyderabad
    
    • And read it into a relation student using the LOAD operator as shown below.
    grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt' USING PigStorage(',')
                        as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray );
    
    • Now, describe the relation named student and verify the schema as shown below.
     grunt> describe student;
    
    • Once you execute the above Pig Latin statement, it will produce the following output.
    grunt> student: { id: int,firstname: chararray,lastname: chararray,phone: chararray,city: chararray }
    

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