Apache Pig Union运算符

由 jarodhu 创建，youj 最后一次修改 2016-12-28 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。语法下面给出了 UNION 运算符的语法。grunt> Relation_name3 = UNION Relation_name1, Relation_name2;例假设在HDFS的 /pig_data/ 目录中有两个文件，即 student_data1.txt 和 student_data2.txt ，如下所示。 Student_data1.txt 001,Rajiv,Reddy,9848022337,Hyderabad002,siddarth,Battacharya,9848022338,Kolkata003,Rajesh,Khanna,9848022339,Delhi004,Preethi,Agarwal,9848022330,Pune005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar006,Archana,Mishra,9848022335,Chennai. Student_data2.txt 7,Komal,Nayak,9848022334,trivendram.8,Bharathi,Nambiayar,9848022333,Chennai.将这两个文件加载到Pig中，通过关系 student1 和 student2 ，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;验证使用 DUMP 运算子验证关系student，如下所示。grunt> Dump student; 输出它将显示以下输出，显示关系student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)