05hive function

A system built-in function

1) Check the system comes with a function hive> show functions;

2) a function of displaying the usage hive comes> desc function upper;

3) the use of a detailed display function comes hive> desc function extended upper;

II. Customizing functions

1. Category

1.1 User-defined functions are divided into the following three categories:

(1) UDF (User-Defined-Function) into a one

(2) UDAF (User-Defined Aggregation Function) aggregate function, into a plurality

Similar to: count / max / min

(3) UDTF (User-Defined Table-Generating Functions) a Multiple-Out

The lateral view explore ()

1.2 official document address

https://cwiki.apache.org/confluence/display/Hive/HivePlugins

1.3 Programming Steps

(1) inherited org.apache.hadoop.hive.ql.UDF

(2) the need to achieve evaluate function; evaluate support function overloading;

(3) create a function in hive command line window

a) 添加 jar add jar linux_jar_path

b）创建 function create [temporary] function [dbname.]function_name AS class_name;

(4) Delete function in the hive command line window

Drop [temporary] function [if exists] [dbname.]function_name;

Note: UDF must have a return type, can return null, but can not return type is void;

2. Custom UDF function

1) create a Maven project Hive

2) introducing dependent

<dependencies>  

<!-- https://mvnrepository.com/artifact/org.apache.hive/hive-exec -->  

<dependency>   

<groupId>org.apache.hive</groupId>   

<artifactId>hive-exec</artifactId>   

<version>1.2.1</version>  

</dependency>

</dependencies>

3) Create a class

package com.atguigu.hive;

import org.apache.hadoop.hive.ql.exec.UDF;

 

public class Lower extends UDF {

 

      public String evaluate (String s) {

     if (s == null) {   

return null;  

}     

return s.toLowerCase(); 

}

}