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https://issues.apache.org/jira/browse/SPARK-27123?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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DB Tsai resolved SPARK-27123.
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Resolution: Fixed
Fix Version/s: 3.0.0
Issue resolved by pull request 24049
[https://github.com/apache/spark/pull/24049]
> Improve CollapseProject to handle projects cross limit/repartition/sample
> -------------------------------------------------------------------------
>
> Key: SPARK-27123
> URL: https://issues.apache.org/jira/browse/SPARK-27123
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Dongjoon Hyun
> Assignee: Dongjoon Hyun
> Priority: Major
> Fix For: 3.0.0
>
>
> `CollapseProject` optimizer simplifies the plan by merging the adjacent
> projects and performing alias substitution.
> {code:java}
> scala> sql("SELECT b c FROM (SELECT a b FROM t)").explain
> == Physical Plan ==
> *(1) Project [a#5 AS c#1]
> +- Scan hive default.t [a#5], HiveTableRelation `default`.`t`,
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#5]
> {code}
> We can do that more complex cases like the following.
> *BEFORE*
> {code:java}
> scala> sql("SELECT b c FROM (SELECT /*+ REPARTITION(1) */ a b FROM
> t)").explain
> == Physical Plan ==
> *(2) Project [b#0 AS c#1]
> +- Exchange RoundRobinPartitioning(1)
> +- *(1) Project [a#5 AS b#0]
> +- Scan hive default.t [a#5], HiveTableRelation `default`.`t`,
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#5]
> {code}
> *AFTER*
> {code:java}
> scala> sql("SELECT b c FROM (SELECT /*+ REPARTITION(1) */ a b FROM
> t)").explain
> == Physical Plan ==
> Exchange RoundRobinPartitioning(1)
> +- *(1) Project [a#11 AS c#7]
> +- Scan hive default.t [a#11], HiveTableRelation `default`.`t`,
> org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe, [a#11]
> {code}
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