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https://issues.apache.org/jira/browse/FLINK-9422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16493560#comment-16493560
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Ruidong Li commented on FLINK-9422:
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[~fhueske], I'm working on the issue. I have some questions about the first
implementation.
1. How does a user specify the implementation? It may works with rowtime but
the user want to materialize all distinct values.
2. What if the user want to hold the data for his preferred time? may be
longer than two watermarks.
> Dedicated operator for UNION on streaming tables with time attributes
> ---------------------------------------------------------------------
>
> Key: FLINK-9422
> URL: https://issues.apache.org/jira/browse/FLINK-9422
> Project: Flink
> Issue Type: Improvement
> Components: Table API & SQL
> Reporter: Fabian Hueske
> Assignee: Ruidong Li
> Priority: Minor
>
> We can implement a dedicated operator for a {{UNION}} operator on tables with
> time attributes. Currently, {{UNION}} is translated into a {{UNION ALL}} and
> a subsequent {{GROUP BY}} on all attributes without aggregation functions.
> The state of the grouping operator is only clean up using state retention
> timers.
> The dedicated operator would leverage the monotonicity property of the time
> attribute and watermarks to automatically clean up its state.
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