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https://issues.apache.org/jira/browse/FLINK-22894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17358309#comment-17358309
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JING ZHANG commented on FLINK-22894:
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[~alpinegizmo] Thanks for reporting the bug. I would like to fix it soon.
> Window Top-N should allow n=1
> -----------------------------
>
> Key: FLINK-22894
> URL: https://issues.apache.org/jira/browse/FLINK-22894
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Runtime
> Affects Versions: 1.13.1
> Reporter: David Anderson
> Priority: Major
>
> I tried to reimplement the Hourly Tips exercise from the DataStream training
> using Flink SQL. The objective of this exercise is to find the one taxi
> driver who earned the most in tips during each hour, and report that driver's
> driverId and the sum of their tips.
> This can be expressed as a window top-n query, where n=1, as in
> {{FROM (}}
> {{ SELECT *, ROW_NUMBER() OVER }}{{(PARTITION BY window_start, window_end
> ORDER BY sumOfTips DESC) as rownum}}
> {{ FROM ( }}
> {{ SELECT driverId, window_start, window_end, sum(tip) as sumOfTips}}
> {{ FROM TABLE( }}
> {{ TUMBLE(TABLE fares, DESCRIPTOR(startTime), INTERVAL '1' HOUR))}}
> {{ GROUP BY driverId, window_start, window_end}}
> {{ )}}
> {{) WHERE rownum = 1;}}
>
> This fails because the {{WindowRankOperatorBuilder}} insists on {{rankEnd >
> 1. }}So, in other words, while it is possible to report the top 2 drivers, or
> the driver in 2nd place, it's not possible to report only the top driver.
> This appears to be an off-by-one error in the range checking.
>
>
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