[jira] [Commented] (KYLIN-2620) Check for "ORDER BY LIMIT" clause when rewrite SUM query as TOPN

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KYLIN-2620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16778974#comment-16778974 ] 

ASF GitHub Bot commented on KYLIN-2620:
---------------------------------------

Wayne1c commented on pull request #489: KYLIN-2620 Make the condition stricter to answer query with topN
URL: https://github.com/apache/kylin/pull/489
 
 
   
 
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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: Shaofeng SHI
>            Priority: Major
>             Fix For: v2.6.1
>
>
> 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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