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https://issues.apache.org/jira/browse/HIVE-5358?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13780765#comment-13780765
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Chun Chen commented on HIVE-5358:
---------------------------------
Thanks, [~yhuai]. I got it. Seems like the first method "adjust the first GBY
to construct its key from both key and value of the reduce input" is easier and
don't have to waste extra resources to sort the rows.
> ReduceSinkDeDuplication should ignore column orders when check overlapping
> part of keys between parent and child
> ----------------------------------------------------------------------------------------------------------------
>
> Key: HIVE-5358
> URL: https://issues.apache.org/jira/browse/HIVE-5358
> Project: Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Chun Chen
> Assignee: Chun Chen
> Attachments: D13113.1.patch, HIVE-5358.2.patch, HIVE-5358.patch
>
>
> {code}
> select key, value from (select key, value from src group by key, value) t
> group by key, value;
> {code}
> This can be optimized by ReduceSinkDeDuplication
> {code}
> select key, value from (select key, value from src group by key, value) t
> group by value, key;
> {code}
> However the sql above can't be optimized by ReduceSinkDeDuplication currently
> due to different column orders of parent and child operator.
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