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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:
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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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