📅 最后修改于: 2020-12-02 05:36:28 🧑 作者: Mango
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。
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。
Student_data1.txt
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.
Student_data2.txt
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运算符符合并这两个关系的内容，如下所示。
grunt> student = UNION student1, student2;
如下所示，使用DUMP运算符验证关系学生。
grunt> Dump student;
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)