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https://issues.apache.org/jira/browse/FLINK-23747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17412967#comment-17412967
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Xintong Song commented on FLINK-23747:
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[~liliwei],
I'm not an expert in this area, thus I cannot comment on what you've raised.
Maybe [~qingru zhang] and [~jark] can advise on this.
You absolutely can open another issue to have the discussion and track this.
> Testing Window TVF offset
> -------------------------
>
> Key: FLINK-23747
> URL: https://issues.apache.org/jira/browse/FLINK-23747
> Project: Flink
> Issue Type: Improvement
> Components: Tests
> Reporter: JING ZHANG
> Assignee: liwei li
> Priority: Blocker
> Labels: release-testing
> Fix For: 1.14.0
>
>
> Window offset is an optional parameter which could be used to change the
> alignment of windows.
> There are something we need clarify about window offset:
> (1) In SQL, window offset is an optional parameter, if it is specified, it is
> the last parameter of the window.
> for Tumble window
> {code:java}
> TUMBLE(TABLE MyTable, DESCRIPTOR(rowtime), INTERVAL '15' MINUTE, INTERVAL '5'
> MINUTE){code}
> for Hop Window
> {code:java}
> HOP(TABLE MyTable, DESCRIPTOR(rowtime), INTERVAL '1' MINUTE, INTERVAL '15'
> MINUTE,
> INTERVAL '5' MINUTE){code}
> for Cumulate Window
> {code:java}
> CUMULATE(TABLE MyTable, DESCRIPTOR(rowtime), INTERVAL '1' MINUTE, INTERVAL
> '15' MINUTE, INTERVAL '5' MINUTE){code}
> (2) Window offset could be positive duration and negative duration.
> (3) Window offset is used to change the alignment of Windows. The same record
> may be assigned to the different window after set window offset. But it
> always apply a rule, timestamp >= window_start && timestamp < window_end.
> Give a demo, for a tumble window, window size is 10 MINUTE, which window
> would be assigned to for a record with timestamp 2021-06-30 00:00:04?
> # offset is '-16 MINUTE', the record assigns to window [2021-06-29
> 23:54:00, 2021-06-30 00:04:00)
> # offset is '-6 MINUTE', the record assigns to window [2021-06-29 23:54:00,
> 2021-06-30 00:04:00)
> # offset is '-4 MINUTE', the record assigns to window [2021-06-29 23:56:00,
> 2021-06-30 00:06:00)
> # offset is '0', the record assigns to window [2021-06-30 00:00:00,
> 2021-06-30 00:10:00)
> # offset is '4 MINUTE', the record assigns to window [2021-06-29 23:54:00,
> 2021-06-30 00:04:00)
> # offset is '6 MINUTE, the record assigns to window [2021-06-29 23:56:00,
> 2021-06-30 00:06:00)
> # offset is '16 MINUTE', the record assigns to window [2021-06-29 23:56:00,
> 2021-06-30 00:06:00)
> (4) We could find that, some window offset parameters may have same effect on
> the alignment of windows, in the above case, '-16 MINUTE' /'-6 MINUTE'/'4
> MINUTE' have same effect on a tumble window with '10 MINUTE' size.
> (5) Window offset is only used to change the alignment of Windows, it has no
> effect on watermark.
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