viirya commented on a change in pull request #31966:
URL: https://github.com/apache/spark/pull/31966#discussion_r602997773
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -241,12 +262,69 @@ object GeneratorNestedColumnAliasing {
// On top on `Generate`, a `Project` that might have nested column
accessors.
// We try to get alias maps for both project list and generator's
children expressions.
val exprsToPrune = projectList ++ g.generator.children
- NestedColumnAliasing.getAliasSubMap(exprsToPrune,
g.qualifiedGeneratorOutput).map {
+ NestedColumnAliasing.getAliasSubMap(exprsToPrune).map {
case (nestedFieldToAlias, attrToAliases) =>
// Defer updating `Generate.unrequiredChildIndex` to next round of
`ColumnPruning`.
- val newChild =
- NestedColumnAliasing.replaceWithAliases(g, nestedFieldToAlias,
attrToAliases)
- Project(NestedColumnAliasing.getNewProjectList(projectList,
nestedFieldToAlias), newChild)
+
+ val (nestedFieldsOnGenerator, nestedFieldsNotOnGenerator) =
+ nestedFieldOnGeneratorOutput(nestedFieldToAlias,
g.qualifiedGeneratorOutput)
+ val (attrToAliasesOnGenerator, attrToAliasesNotOnGenerator) =
+ aliasesOnGeneratorOutput(attrToAliases, g.qualifiedGeneratorOutput)
+
+ // Push nested column accessors through `Generator`. We cannot prune
on `Generator`'s
+ // output.
+ val newChild = NestedColumnAliasing.replaceWithAliases(g,
+ nestedFieldsNotOnGenerator, attrToAliasesNotOnGenerator)
+ val pushedThrough = Project(NestedColumnAliasing
+ .getNewProjectList(projectList, nestedFieldsNotOnGenerator),
newChild)
+
+ // Pruning on `Generator`'s output. We only process single field
case.
+ // For multiple field case, we cannot directly move field extractor
into
+ // the generator expression. A workaround is to re-construct array
of struct
+ // from multiple fields. But it will be more complicated and may not
worth.
+ if (nestedFieldsOnGenerator.size == 1) {
+ // Only one nested column accessor.
+ // E.g., df.select(explode($"items").as("item")).select($"item.a")
+ pushedThrough match {
+ case p @ Project(_, newG: Generate) =>
+ // Replace the child expression of `ExplodeBase` generator with
+ // nested column accessor.
+ // E.g., df.select(explode($"items").as("item")) =>
+ // df.select(explode($"items.a").as("item"))
+ val rewrittenG = newG.transformExpressions {
+ case e: ExplodeBase =>
+ val extractor =
nestedFieldsOnGenerator.head._1.transformUp {
+ case _: Attribute =>
+ e.child
+ case g: GetStructField =>
+ ExtractValue(g.child, Literal(g.extractFieldName),
SQLConf.get.resolver)
Review comment:
let me add one.
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