Pig ORDER BY 运算符



  • ORDER BY 运算符

    Pig Latin的ORDER BY运算符用于基于一个或多个字段的排序顺序来显示关系的内容。
    句法
    下面给出的是ORDER BY运算符的语法。
    
    grunt> Relation_name2 = ORDER Relatin_name1 BY (ASC|DESC);
    
    
    假设我们在HDFS目录/pig_data/中有一个名为student_details.txt的文件,如下所示。
    
    001,Rajiv,Reddy,21,9848022337,Hyderabad
    002,siddarth,Battacharya,22,9848022338,Kolkata
    003,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
    
    
    并且我们已经将该文件加载到Pig中,关系名称为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,并使用ORDER BY运算符将其存储到另一个名为order_by_data的关系中,如下所示。
    
    grunt> order_by_data = ORDER student_details BY age DESC;
    
    
    验证
    如下所示,使用DUMP运算符验证关系order_by_data。
    
    grunt> Dump order_by_data; 
    
    
    输出
    它将产生以下输出,显示关系order_by_data的内容。
    
    (8,Bharathi,Nambiayar,24,9848022333,Chennai)
    (7,Komal,Nayak,24,9848022334,trivendram)
    (6,Archana,Mishra,23,9848022335,Chennai) 
    (5,Trupthi,Mohanthy,23,9848022336,Bhuwaneshwar)
    (3,Rajesh,Khanna,22,9848022339,Delhi) 
    (2,siddarth,Battacharya,22,9848022338,Kolkata)
    (4,Preethi,Agarwal,21,9848022330,Pune) 
    (1,Rajiv,Reddy,21,9848022337,Hyderabad)