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https://issues.apache.org/jira/browse/SPARK-16208?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun reopened SPARK-16208:
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I made a new PR.
> Add `CollapseEmptyPlan` optimizer
> ---------------------------------
>
> Key: SPARK-16208
> URL: https://issues.apache.org/jira/browse/SPARK-16208
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Dongjoon Hyun
> Assignee: Apache Spark
> Priority: Minor
>
> This PR adds a new logical optimizer, `CollapseEmptyPlan`, to collapse a
> logical plans consisting of only empty LocalRelations. The only exceptional
> logical plan is aggregation. For aggregation plan, only simple cases are
> consider for this optimization.
> **Before**
> {code}
> scala> sql("select a from values (1,2) T(a,b) where 1=0 group by a,b having
> a>1 order by a,b").explain
> == Physical Plan ==
> *Project [a#11]
> +- *Sort [a#11 ASC, b#12 ASC], true, 0
> +- Exchange rangepartitioning(a#11 ASC, b#12 ASC, 200)
> +- *HashAggregate(keys=[a#11, b#12], functions=[])
> +- Exchange hashpartitioning(a#11, b#12, 200)
> +- *HashAggregate(keys=[a#11, b#12], functions=[])
> +- LocalTableScan <empty>, [a#11, b#12]
> {code}
> **After**
> {code}
> scala> sql("select a from values (1,2) T(a,b) where 1=0 group by a,b having
> a>1 order by a,b").explain
> == Physical Plan ==
> LocalTableScan <empty>, [a#0]
> {code}
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