Pig Union 运算符

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  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;
  

  例

  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)