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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23375) Optimizer should remove unneeded Sort
Date Sat, 08 Dec 2018 04:10:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16713516#comment-16713516
] 

Apache Spark commented on SPARK-23375:
--------------------------------------

User 'seancxmao' has created a pull request for this issue:
https://github.com/apache/spark/pull/23258

> Optimizer should remove unneeded Sort
> -------------------------------------
>
>                 Key: SPARK-23375
>                 URL: https://issues.apache.org/jira/browse/SPARK-23375
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Marco Gaido
>            Assignee: Marco Gaido
>            Priority: Minor
>             Fix For: 2.4.0
>
>
> As pointed out in SPARK-23368, as of now there is no rule to remove the Sort operator
on an already sorted plan, ie. if we have a query like:
> {code}
> SELECT b
> FROM (
>     SELECT a, b
>     FROM table1
>     ORDER BY a
> ) t
> ORDER BY a
> {code}
> The sort is actually executed twice, even though it is not needed.



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