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https://issues.apache.org/jira/browse/FLINK-19830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17732978#comment-17732978
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Robert Metzger commented on FLINK-19830:
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Awesome, thanks for the update!
> Properly implements processing-time temporal table join
> -------------------------------------------------------
>
> Key: FLINK-19830
> URL: https://issues.apache.org/jira/browse/FLINK-19830
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Runtime
> Reporter: Leonard Xu
> Assignee: Leonard Xu
> Priority: Major
>
> The exsiting TemporalProcessTimeJoinOperator has already supported temporal
> table join.
> However, the semantic of this implementation is problematic, because the
> join processing for left stream doesn't wait for the complete snapshot of
> temporal table, this may mislead users in production environment.
> Under the processing time temporal join semantics, to get the complete
> snapshot of temporal table may need introduce new mechanism in FLINK SQL in
> the future.
> **Background** :
> * The reason why we turn off the switch[1] for `FOR SYSTEM_TIME AS OF`
> syntax for *temporal table join* is only the semantic consideration as above.
> * The reason why we turn on *temporal table function* is that it has been
> alive for a long time, thus although it exists same semantic problem, but we
> still support it from the perspective of compatibility.
> [1]
> [https://github.com/apache/flink/blob/4fe9f525a92319acc1e3434bebed601306f7a16f/flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/plan/nodes/exec/stream/StreamExecTemporalJoin.java#L257]
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