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https://issues.apache.org/jira/browse/HIVE-6348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16040710#comment-16040710
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Rui Li commented on HIVE-6348:
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Hi [~xuefuz], [~vgarg], I also think it's easier to do this in AST. Once we
have the OP tree, I'm not sure how to tell whether an order by belongs to sub
queries. Besides, I also noted CBO may introduce synthetic sub queries. So I'll
write a patch to do it in AST.
> Order by/Sort by in subquery
> ----------------------------
>
> Key: HIVE-6348
> URL: https://issues.apache.org/jira/browse/HIVE-6348
> Project: Hive
> Issue Type: Bug
> Reporter: Gunther Hagleitner
> Assignee: Rui Li
> Priority: Minor
> Labels: sub-query
> Attachments: HIVE-6348.1.patch, HIVE-6348.2.patch
>
>
> select * from (select * from foo order by c asc) bar order by c desc;
> in hive sorts the data set twice. The optimizer should probably remove any
> order by/sort by in the sub query unless you use 'limit '. Could even go so
> far as barring it at the semantic level.
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