dongjoon-hyun commented on a change in pull request #24637: [SPARK-27707][SQL]
Prune unnecessary nested fields from Generate in explode
URL: https://github.com/apache/spark/pull/24637#discussion_r300880428
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -588,6 +588,16 @@ object ColumnPruning extends Rule[LogicalPlan] {
.map(_._2)
p.copy(child = g.copy(child = newChild, unrequiredChildIndex =
unrequiredIndices))
+ // prune unrequired nested fields
+ case p @ Project(projectList, g: Generate) if
SQLConf.get.nestedSchemaPruningEnabled =>
+ NestedColumnAliasing.getAliasSubMap(projectList).map {
+ case (nestedFieldToAlias, attrToAliases) =>
+ val newChild = g.withNewChildren(g.children.map { child =>
+ Project(child.output ++ attrToAliases.values.flatten, child)
Review comment:
This looks addition instead of a replacing. So, this may optimize `explode`,
but we cannot avoid the full scan of underlying parquet files?
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