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https://issues.apache.org/jira/browse/FLINK-19830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17732976#comment-17732976
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Jark Wu commented on FLINK-19830:
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Hi [~rmetzger], sorry for the late reply. Yes, your understanding of the
Processing Time Temporal Join is correct. But this is not the same limitation
with Event Time Temporal Join, because the probe side will wait for the build
side based on the watermark, so there won't be wrong unmatched records emitted
for event time join.
Currently, we have some plans to support some kind of custom event mechanism to
support this feature in the near time. Hope I can be back with more information
soon!
> 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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