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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-672) Re-enable user defined aggregates
Date Tue, 10 May 2011 18:51:48 GMT

    [ https://issues.apache.org/jira/browse/DERBY-672?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13031306#comment-13031306
] 

Rick Hillegas commented on DERBY-672:
-------------------------------------

The SQL Server syntax for user-defined aggregates can be found here: http://msdn.microsoft.com/en-us/library/ms182741.aspx
and http://msdn.microsoft.com/en-us/library/ms131051.aspx In summary, you bind an external
class to an aggregate name. The class must satisfy a contract, which requires it to have methods
to initialize, aggregate, merge, and terminate:

CREATE AGGREGATE [<schemaName>.]<aggregateName> ( <functionParameter> [,
<functionParameter> ] * )
RETURNS <returnDataType>
EXTERNAL NAME <className>

where <functionParameter> is as defined for CREATE FUNCTION (a parameter name followed
by a dataType)

and <className> implements the following methods:

public void init();
public void accumulate( <methodParameter> [, <methodParameter> ] *);  // method
parameters correspond to function parameters above
public void merge( <className> otherAggregator );
public <returnType> terminate();  // returnType corresponds to returnDataType above




> Re-enable user defined aggregates
> ---------------------------------
>
>                 Key: DERBY-672
>                 URL: https://issues.apache.org/jira/browse/DERBY-672
>             Project: Derby
>          Issue Type: Improvement
>          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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