db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Rick Hillegas <rick.hille...@oracle.com>
Subject Re: varargs functions: primitive or Object type?
Date Mon, 06 Jan 2014 15:34:16 GMT
On 1/6/14 6:09 AM, Rick Hillegas wrote:
> On 1/6/14 4:47 AM, Tim Dudgeon wrote:
>> I'm trying to write a function that performs aggregation and I'm not 
>> clear on how to handle the varargs part.
>> Lets assume I was wanting to write a function that does averaging, 
>> and handles null values correctly.
>> I'm defining my function like this:
>>
>> CREATE FUNCTION MYAVG
>> ( VALS DOUBLE ... )
>> RETURNS DOUBLE
>> PARAMETER STYLE DERBY
>> NO SQL LANGUAGE JAVA
>> EXTERNAL NAME 'myorg.misc.derby.functions.MyFunctions.myAverage;
>>
>>
>> What does the signature of the Java method need to be?
>> I've tried:
>>
>> static Double myAverage(Double[] vals) { }
>> static Double myAverage(Double... vals) { }
>>
>> Both of these fail with:
>> java.sql.SQLSyntaxErrorException: No method was found that matched 
>> the method call 
>> myorg.misc.derby.functions.MyFunctions.myAverage(double...), tried 
>> all combinations of object and primitive types and any possible type 
>> conversion for any  parameters the method call may have
>>
>> Seems like its wanting
>> static Double myAverage(double... vals) { }
>> but if that's the case how are nulls handled?
>>
>> Thanks
>> Tim
>>
>>
>>
> Thanks for tripping across this, Tim. Looks like there's a bug in 
> here. Works for Integer args but not Double args. Stand by while I 
> take a look...
>
> Thanks,
> -Rick
>
Hi Tim,

Well, I'm puzzled. Now I can't reproduce the problem I thought I was 
seeing. I have written a script which tests all possible datatypes with 
varargs. The script runs cleanly. The following small test case works 
too. Compile the following class...

public class ww
{
     public  static  Double doubleAverage( Double... vals )
     {
         double result = 0;

         for ( Double val : vals )
         {
             result += val.doubleValue();
         }

         return result / vals.length;
     }
}

...then the following script runs cleanly for me...

connect 'jdbc:derby:memory:db;create=true';

create function doubleAverage( vals double... ) returns double
language java parameter style derby no sql
external name 'ww.doubleAverage';

values doubleAverage( 1.11, 2.22, 3.33 );

values doubleAverage( 1.0, 2.0, 3.0 );

Maybe your problem is that your methods are not public.

By the way: If your ultimate problem is an aggregation problem, you may 
be interested in the user defined aggregates feature which was 
introduced by release 10.10.1: 
http://db.apache.org/derby/docs/10.10/devguide/cdevspecialuda.html

Hope this helps,
-Rick


Mime
View raw message