Marco Gaido created SPARK-23375:
-----------------------------------

             Summary: 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


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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