[jira] [Created] (SPARK-27123) Improve CollapseProject to handle projects cross limit/repartition/sample

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

Dongjoon Hyun created SPARK-27123:
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             Summary: 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: Improvement
          Components: SQL
    Affects Versions: 3.0.0
            Reporter: Dongjoon Hyun


`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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