[jira] [Commented] (SPARK-23375) Optimizer should remove unneeded Sort

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-23375?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16358435#comment-16358435 ] 

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

User 'mgaido91' has created a pull request for this issue:
https://github.com/apache/spark/pull/20560

> 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
>            Priority: Minor
>
> 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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