Re: User Defined Aggregations in MonetDB?

This involves actually two steps. 1) SQL to MAL connection Example: CREATE AGGREGATE myagg (b INTEGER) RETURNS INTEGER EXTERNAL NAME mymodule.meagg; 2) MAL to C connection module mymodule; command meagg(b:bat[:oid,:int], e:bat[:oid,:int]) :bat[:oid,:int] address meagg_c_implementation comment "Meagg mal aggregate"; str meagg_c(int *retid, int *bid, int *eid) { /* C code here */ } The code is quite self-explanatory I think. Hope that helps, Babis On Tue, Nov 19, 2013 at 7:16 PM, Alastair McKinley wrote:

Hi Babis,

Thanks for your guidance that is very useful indeed!

I am not entirely clear on how a specific SUM aggregate query maps to a particular MAL signature/C function in aggr.mal.

For example, if I had

CREATE TABLE T ( int a, float b, float c );

SELECT a,SUM(b+c) FROM T GROUP BY a;

What MAL function signature would this result in?

Best regards and thanks,

Alastair ________________________________________ From: users-list on behalf of Charalampos Nikolaou Sent: 19 November 2013 14:15 To: Communication channel for MonetDB users Subject: Re: User Defined Aggregations in MonetDB?

Hi Alastair,

sure you can do that. You can have a look at the following files:

http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/monetdb5/modules/kernel/... http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/monetdb5/modules/kernel/... http://dev.monetdb.org/hg/MonetDB/file/af39d1a659f6/gdk/gdk_aggr.c

This article should be helpful and informative as well to you that explains how aggregates and grouping works inside MonetDB: http://www.monetdb.org/content/internal-changes-feb2013-release

Regards, Babis

On Tue, Nov 19, 2013 at 3:42 PM, Alastair McKinley wrote:

...

Dear all,

I was wondering if it is possible to build a User Defined Aggregation in MonetDB.

For example, rather than do SUM(myfunction(a,b)) I would like to do MYAGG(a,b) where MYAGG internally holds a small buffer of a and b values so that they can be calculated in a batch fashion with a high performance batch implementation of the function.

Could MYAGG be implemented in C?

Best regards,

Alastair

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