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https://issues.apache.org/jira/browse/KYLIN-2620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16843389#comment-16843389
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ASF GitHub Bot commented on KYLIN-2620:
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Wayne1c commented on pull request #647: KYLIN-2620 TopN can't match when multi
sort columns
URL: https://github.com/apache/kylin/pull/647
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> Check for "ORDER BY LIMIT" clause when rewrite SUM query as TOPN
> ----------------------------------------------------------------
>
> Key: KYLIN-2620
> URL: https://issues.apache.org/jira/browse/KYLIN-2620
> Project: Kylin
> Issue Type: Bug
> Components: Measure - TopN
> Reporter: Lin Tingmao
> Assignee: Chao Long
> Priority: Major
> Fix For: Future, v3.0.0
>
> Attachments: cube_desc.png, sql.png
>
>
> When running the following query
> select sum(measure) from table group by col_id
> if there exists TOPN(measure, group by col_id) measure,
> TopNMeasureType.isTopNCompatibleSum() will pass, so the SUM is rewritten
> to TOPN. This confuses the user since they may expect a accurate result for
> every distinct value of group by column(s).
> Kylin should check if "ORDER BY col_id LIMIT topncapacity" is present in the
> query to determine whether to rewrite.
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