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