describe 运算符用于查看关系的架构.
语法描述运算符如下 :
grunt> Describe Relation_name
假设我们在HDFS中有一个文件 student_data.txt 以下内容.
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.
我们已经使用LOAD运算符将其读入关系 student ,如下所示.
grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt' USING PigStorage(',') as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray );
现在,让我们描述名为 student 的关系并验证架构,如下所示.
runt> describe student;
行上面的Pig Latin语句后,它将产生以下输出。
grunt> student: { id: int,firstname: chararray,lastname: chararray,phone: chararray,city: chararray }