00-CusomHiveEvalUDF-NVL2

This gist covers a simple Hive eval UDF in Java, that mimics NVL2 functionality in Oracle.
NVL2 is used to handle nulls and conditionally substitute values.
 
Included:
1.  Input data
2.  Expected results
3.  UDF code in java
4.  Hive query to demo the UDF
5.  Output

Note: The dataset is very small - as the purpose of this gist is instructional.  :)

About the NVL2 functionality in this demo:
------------------------------------------
Return type: String
Parameters: Three comma separated strings, we will refer to as:
expr1, expr2, expr3
Purpose: If expr1 is null, NVL2 returns expr3, otherwise, expr3

01-InputData

**************************
Input data
**************************

1. Execute locally on the node you are running Hive client from
-----------------------------------------------------------------
Create input file/data to use for the demo.
Since this gist is merely for instructional purpose, the dataset is small.

cd ~
mkdir hiveProject
cd hiveProject
vi Departments_UDFTest

Paste this..ensuring the fields are delimited by tabs and record with new line.
d001	Marketing
d002	Finance
d003	Human Resources
d004	Production
d005	Development
d006	Quality Management
d007	Sales
d008
d009	Customer Service

2.  Hadoop commands
--------------------
hadoop fs -mkdir hiveProject
hadoop fs -put hiveProject/Departments_UDFTest hiveProject

02-HiveTableSetup

*********************************************
Setting up the Hive table
*********************************************
In hive shell....

a) Create table:

CREATE EXTERNAL TABLE IF NOT EXISTS departments_UDFTest
(
deptNo String,
deptName String
)
Row format delimited
fields terminated by '\t'
LOCATION '/user/akhanolk/hiveProject';

b) Quick test:

Select * from departments_UDFTest;

d001	Marketing
d002	Finance
d003	Human Resources
d004	Production
d005	Development
d006	Quality Management
d007	Sales
d008	NULL
d009	Customer Service

03-UDFCode

//------------------------------------------------------------------
// Filename: NVL2.java
//------------------------------------------------------------------

package khanolkar.HiveUDFs;

import java.io.IOException;
import org.apache.hadoop.hive.ql.exec.UDF;

public class NVL2 extends UDF {
        String expr1, expr2, expr3;

	public NVL2() {
	}

	public String evaluate(String pExpr1, String pExpr2, String pExpr3)
			throws IOException {

		try {

			expr1 = (String) pExpr1;
			expr2 = (String) pExpr2;
			expr3 = (String) pExpr3;

			return (expr1 != null ? expr2 : expr3);

		} catch (Exception e) {
			// Cause task failure
			throw new IOException("Error with Hive UDF, NVL2!", e);
		}
	}

}

04-ExpectedResults

****************************
Expected results
****************************

Query: 
select deptNo,NVL2(deptName,deptName,'Procrastrination') from departments_UDFTest;

The null in the department name for department d008, should be returned as "Procrastrination".
For the rest of the records, the query should return the data in Hive, as is.

 

05-HiveTest

*******************************
Testing the UDF
*******************************

hive> add jar hiveProject/jars/NVL2.jar;

hive> CREATE TEMPORARY FUNCTION NVL2
 AS 'khanolkar.HiveUDFs.NVL2';

hive> select deptNo,NVL2(deptName,deptName) from departments_UDFTest;                   
FAILED: SemanticException [Error 10014]: Line 1:14 Wrong arguments 'deptName': No matching method for class khanolkar.HiveUDFs.NVL2 with (string, string). Possible choices: _FUNC_(string, string, string) 

hive> select deptNo,NVL2(deptName,deptName,'Procrastrination') from departments_UDFTest;
OK
d001	Marketing
d002	Finance
d003	Human Resources
d004	Production
d005	Development
d006	Quality Management
d007	Sales
d008	Procrastrination
d009	Customer Service