Users who want to take the advantage of the UDF capability can create UDF functions using the following syntax:

CREATE FUNCTION [ owner_name.]udf_name ( [ parameter_decl [ , ... ] ] )
			RETURN data_type 
			[IMPORT java_import_clause ]
	BEGIN
	[ java_snippet  ]
END  
parameter_decl:=  parameter_name data_type

The following example shows how to create a UDF and use it in a SELECT function. In this example, the UDF, which is an EXTRACT function, can be used to return a single part (year, month, day, hour, minute) of a date /time stamp of a certain event. This data could be used to compare or calculate a time period or a certain delay that might have occurred between the two events. 

CREATE function EXTRACT(extractfield varchar(20), col timestamp)
return integer
import 
import java.util.Date;
begin 
extractfield=extractfield.toLowerCase();
switch(extractfield)
{
    case "date" : return col.getDate(); 
    case "month" : return col.getMonth(); 
    case "year" : return col.getYear();
    case "time" : return (int)col.getTime(); 
    case "minute" : return (int)col.getMinutes();
    case "hour" : return (int)col.getHours();
    case "second" : return (int)col.getSeconds();
    case "day" : return col.getDay();
    case "default" : return -1; 
}
return 1;
end

The above UDF can be called using the SELECT function as shown in the following example:

SELECT EXTRACT('date' , orderdate) from pub.order;
EXTRACT(date,OrderDate)
-----------------------
                      9
                     27
SELECT EXTRACT('day' , orderdate) from pub.order;
EXTRACT(day,OrderDate)
----------------------
                     3
                     5
SELECT EXTRACT('month' , orderdate) from pub.order;
EXTRACT(month,OrderDate)
------------------------
                       1
                       2