Apache Pig 简明教程

Apache Pig - Union Operator

Pig Latin 的 UNION 运算符用于合并两个关系的内容。要在两个关系上执行 UNION 操作,它们的列和域必须相同。

Syntax

下面给出了 UNION 运算符的语法。

grunt> Relation_name3 = UNION Relation_name1, Relation_name2;

Example

假设我们在 HDFS 的 /pig_data/ 目录中具有两个文件 student_data1.txtstudent_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.

我们已使用关系 student1student2 将这两个文件加载到 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;

Verification

使用 DUMP 运算符验证关系 student ,如下所示。

grunt> Dump student;

Output

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)