Pig Union 运算符



  • Union 运算符

    Pig Latin的UNION运算符用于合并两个关系的内容。要对两个关系执行UNION操作,它们的列和域必须相同。
    句法
    下面给出的是UNION运算符的语法。
    
    grunt> Relation_name3 = UNION Relation_name1, Relation_name2;
    
    
    假设我们在HDFS的/pig_data/目录中有两个文件,即student_data1.txt和student_data2.txt,如下所示。
    
    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.
    
    
    
    7,Komal,Nayak,9848022334,trivendram.
    8,Bharathi,Nambiayar,9848022333,Chennai.
    
    
    并将这两个文件通过关系Student1和Student2加载到Pig中,如下所示。
    
    grunt> student1 = LOAD 'hdfs://localhost:9000/pig_data/student_data1.txt' USING PigStorage(',') 
       as (id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray); 
     
    grunt> student2 = LOAD 'hdfs://localhost:9000/pig_data/student_data2.txt' USING PigStorage(',') 
       as (id:int, firstname:chararray, lastname:chararray, phone:chararray, city:chararray);
    
    
    现在,让我们使用UNION运算符合并这两个关系的内容,如下所示。
    
    grunt> student = UNION student1, student2;
    
    
    验证
    如下所示,使用DUMP运算符验证student学生。
    
    grunt> Dump student; 
    
    
    输出
    它将显示以下输出,显示关联学生的内容。
    
    (1,Rajiv,Reddy,9848022337,Hyderabad) (2,siddarth,Battacharya,9848022338,Kolkata)
    (3,Rajesh,Khanna,9848022339,Delhi)
    (4,Preethi,Agarwal,9848022330,Pune) 
    (5,Trupthi,Mohanthy,9848022336,Bhuwaneshwar)
    (6,Archana,Mishra,9848022335,Chennai) 
    (7,Komal,Nayak,9848022334,trivendram) 
    (8,Bharathi,Nambiayar,9848022333,Chennai)