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From "Vineet Garg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-6348) Order by/Sort by in subquery
Date Wed, 14 Jun 2017 04:38:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-6348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16048697#comment-16048697
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Vineet Garg commented on HIVE-6348:
-----------------------------------

{{HiveSortRemoveRule}} removes HiveSortLimit only if it is created by HiveSortJoinReduceRule
"If it is not created by HiveSortJoinReduceRule, we cannot remove it" {{HiveSortMergeRule}}
seems to merge two HiveSortLimit into one which isn't the case here. So I don't think there
is any existing rule covering this case.

> 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, HIVE-6348.3.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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