[jira] [Created] (SPARK-14830) Add RemoveRepetitionFromGroupExpressions optimizer

["Dongjoon Hyun (JIRA)" <ji...@apache.org>]

Dongjoon Hyun created SPARK-14830:
-------------------------------------

             Summary: Add RemoveRepetitionFromGroupExpressions optimizer
                 Key: SPARK-14830
                 URL: https://issues.apache.org/jira/browse/SPARK-14830
             Project: Spark
          Issue Type: Improvement
          Components: Optimizer
            Reporter: Dongjoon Hyun


This issue aims to optimize GroupExpressions by removing repeating expressions. 

**Before**
{code}
scala> sql("select a from (select explode(array(1,2)) a) T group by a, a, a").explain()
== Physical Plan ==
WholeStageCodegen
:  +- TungstenAggregate(key=[a#5,a#5,a#5], functions=[], output=[a#5])
:     +- INPUT
+- Exchange hashpartitioning(a#5, a#5, a#5, 200), None
   +- WholeStageCodegen
      :  +- TungstenAggregate(key=[a#5,a#5,a#5], functions=[], output=[a#5,a#5,a#5])
      :     +- INPUT
      +- Generate explode([1,2]), false, false, [a#5]
         +- Scan OneRowRelation[]
{code}

**After**
{code}
scala> sql("select a from (select explode(array(1,2)) a) T group by a, a, a").explain()
== Physical Plan ==
WholeStageCodegen
:  +- TungstenAggregate(key=[a#5], functions=[], output=[a#5])
:     +- INPUT
+- Exchange hashpartitioning(a#5, 200), None
   +- WholeStageCodegen
      :  +- TungstenAggregate(key=[a#5], functions=[], output=[a#5])
      :     +- INPUT
      +- Generate explode([1,2]), false, false, [a#5]
         +- Scan OneRowRelation[]
{code}



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