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From "Fabian Hueske (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4832) Count/Sum 0 elements
Date Tue, 01 Nov 2016 20:18:58 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15626549#comment-15626549
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Fabian Hueske commented on FLINK-4832:
--------------------------------------

Currently, a {{DataSetAggregate}} is translated into a {{MapFunction}} followed by a {{GroupReduceFunction}}.
The {{MapFunction}} initializes the aggregates and the {{GroupReduceFunction}} computes the
aggregates.

I think we need to do the following. We need to inject a {{Union}} before the Map with static
data set with a single record, that contains only null values for each field.
The {{CountAggregate}} initializes to {{0}} (which is what we want), all other functions initialize
to {{null}} and ignore the record.


> Count/Sum 0 elements
> --------------------
>
>                 Key: FLINK-4832
>                 URL: https://issues.apache.org/jira/browse/FLINK-4832
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>            Reporter: Timo Walther
>
> Currently, the Table API is unable to count or sum up 0 elements. We should improve DataSet
aggregations for this. Maybe by union the original DataSet with a dummy record or by using
a MapPartition function. Coming up with a good design for this is also part of this issue.



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