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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-672) Re-enable user defined aggregates
Date Tue, 12 Dec 2006 21:00:21 GMT
    [ http://issues.apache.org/jira/browse/DERBY-672?page=comments#action_12457874 ] 
            
Rick Hillegas commented on DERBY-672:
-------------------------------------

I do not see ANSI syntax for this feature. Here is the syntax used by some other databases.

----------------------------------------

Cloudscape 3.5:

CREATE AGGREGATE AggregateName FOR
    { JavaClassName | ClassAlias }

The aliased class has to be an implementation of a Cloudscape interface (COM.cloudscape.aggregates.AggregateDefinition).
That, in turn, means that the class has to implement a couple methods:

accumulate() -- accumulator for non-grouped results
getResult()     -- the final result of the accumulation
merge()          -- accumulator for grouped results

---------------------------------------

Postgres 8.0.0:

CREATE AGGREGATE name (
    BASETYPE = input_data_type,
    SFUNC = sfunc,
    STYPE = state_data_type
    [ , FINALFUNC = ffunc ]
    [ , INITCOND = initial_condition ]
)

Here

SFUNC is the name of an accumulator function
FFUNC is the name of a function which returns the accumulated result

-----------------------------------------------------------

IBM Informix:

CREATE AGGREGATE average
   WITH (
      INIT = initFunction,
      ITER = iterationFunction,
      COMBINE = combinationFunction,
      FINAL = resultFunction
      )

where

initFunction is a function initializing the accumulator
iterationFunction a counting function
combinationFunction an accumulator function
resultFunction a function which returns the accumulated result


> Re-enable user defined aggregates
> ---------------------------------
>
>                 Key: DERBY-672
>                 URL: http://issues.apache.org/jira/browse/DERBY-672
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Rick Hillegas
>
> Nicolas Dufour in an email thread titled "functions and list" started on November 2,
2005 requests the ability to create user defined aggregates.
> This functionality used to be in Cloudscape. It was disabled presumably because it was
considered non-standard. However, most of the machinery needed for this feature is still in
the code. We should re-enable user defined aggregates after we agree on acceptable syntax.

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