pig tutorial - apache pig tutorial - Apache Pig Describe Operator - pig latin - apache pig - pig hadoop
What is describe operator?
- The describe operator is used to view the schema of a relation.
- It Returns the schema of a relation.
- Prints the schema of the relation at standard output
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 }