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Posted to reviews@spark.apache.org by GitBox <gi...@apache.org> on 2019/03/11 05:54:11 UTC
[GitHub] [spark] dongjoon-hyun opened a new pull request #24049:
[SPARK-27123][SQL] Improve CollapseProject to handle projects cross
limit/repartition/sample
dongjoon-hyun opened a new pull request #24049: [SPARK-27123][SQL] Improve CollapseProject to handle projects cross limit/repartition/sample
URL: https://github.com/apache/spark/pull/24049
## What changes were proposed in this pull request?
`CollapseProject` optimizer simplifies the plan by merging the adjacent projects and performing alias substitution.
```scala
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]
```
We can do that more complex cases like the following.
**BEFORE**
```scala
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]
```
**AFTER**
```scala
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]
```
## How was this patch tested?
Pass the Jenkins with the newly added and updated test cases.
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