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https://issues.apache.org/jira/browse/FLINK-19449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17297009#comment-17297009
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Benchao Li commented on FLINK-19449:
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[~laiyijie] IMO, a full-fledged LAG function implementation with `merge`,
`retract` is complex. We cannot assume the records are retracted in the order
of appending, hence just remove the first element when retract maybe not
correct.
In our internal branch, I see a lot of usage of LAG without index. And I just
implement a simplest one which does not support `retract`, `merge`, and the
index either. What do you think?
> LEAD/LAG cannot work correctly in streaming mode
> ------------------------------------------------
>
> Key: FLINK-19449
> URL: https://issues.apache.org/jira/browse/FLINK-19449
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / API, Table SQL / Runtime
> Affects Versions: 1.10.2, 1.11.2
> Reporter: Benchao Li
> Priority: Major
>
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