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https://issues.apache.org/jira/browse/FLINK-7800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16216573#comment-16216573
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Xingcan Cui commented on FLINK-7800:
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Hi [~fhueske], thanks for opening this. I got a question about the join
validation. Why couldn't we "push down" all these checks (e.g., for equi-join
predicate) into the DataStream/DataSet rules and organize them in a flat mode?
> Enable window joins without equi-join predicates
> ------------------------------------------------
>
> Key: FLINK-7800
> URL: https://issues.apache.org/jira/browse/FLINK-7800
> Project: Flink
> Issue Type: Sub-task
> Components: Table API & SQL
> Affects Versions: 1.4.0
> Reporter: Fabian Hueske
> Assignee: Xingcan Cui
>
> Currently, windowed joins can only be translated if they have at least on
> equi-join predicate. This limitation exists due to the lack of a good cross
> join strategy for the DataSet API.
> Due to the window, windowed joins do not have to be executed as cross joins.
> Hence, the equi-join limitation does not need to be enforces (even though
> non-equi joins are executed with a parallelism of 1 right now).
> We can resolve this issue by adding a boolean flag to the
> {{FlinkLogicalJoinConverter}} rule to permit non-equi joins and add such a
> rule to the logical optimization set of the DataStream API.
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