Pig Union 运算符 | Pig 教程

#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。
**语法**
下面给出的是UNION运算符的语法。
```bash
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。
```bash
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。
```bash
grunt> student = UNION student1, student2;
```
**验证**
如下所示，使用DUMP运算符验证student学生。
```bash
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)
```

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