LIMIT 运算符用于从关系中获取有限数量的元组.
语法
给定以下是 LIMIT 运算符的语法.
grunt> Result = LIMIT Relation_name required number of tuples;
示例
假设我们在HDFS中有一个名为 student_details.txt 的文件目录/pig_data/如下所示.
student_details.txt
001,Rajiv,Reddy,21,9848022337,Hyderabad002,siddarth,Battacharya,22,9848022338,Kolkata003,Rajesh,Khanna,22,9848022339,Delhi 004,Preethi,Agarwal,21,9848022330,Pune 005,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar 006,Archana,Mishra,23,9848022335,Chennai 007,Komal,Nayak,24,9848022334,trivendram 008,Bharathi,Nambiayar,24,9848022333,Chennai
我们已将此文件加载到Pig with关系名称 student_details 如下所示.
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);
现在,让我们根据学生的年龄按降序对关系进行排序,并将其存储到另一个名为 limit_data 的关系中 ORDER BY 运算符如下所示.
grunt> limit_data = LIMIT student_details 4;
验证
使用 DUMP limit_data >运算符如下所示.
grunt> Dump limit_data;
输出
它将产生以下输出,显示关系 limit_data 如下.
(1,Rajiv,Reddy,21,9848022337,Hyderabad) (2,siddarth,Battacharya,22,9848022338,Kolkata) (3,Rajesh,Khanna,22,9848022339,Delhi) (4,Preethi,Agarwal,21,9848022330,Pune)