viirya commented on a change in pull request #31966:
URL: https://github.com/apache/spark/pull/31966#discussion_r613809778
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -241,12 +262,68 @@ 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) =>
+ val (nestedFieldsOnGenerator, nestedFieldsNotOnGenerator) =
+ nestedFieldOnGeneratorOutput(nestedFieldToAlias,
g.qualifiedGeneratorOutput)
+ val (attrToAliasesOnGenerator, attrToAliasesNotOnGenerator) =
+ aliasesOnGeneratorOutput(attrToAliases, g.qualifiedGeneratorOutput)
+
+ // Push nested column accessors through `Generator`.
// Defer updating `Generate.unrequiredChildIndex` to next round of
`ColumnPruning`.
- val newChild =
- NestedColumnAliasing.replaceWithAliases(g, nestedFieldToAlias,
attrToAliases)
- Project(NestedColumnAliasing.getNewProjectList(projectList,
nestedFieldToAlias), newChild)
+ 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.
+ // TODO(SPARK-34956): support multiple fields.
+ if (nestedFieldsOnGenerator.size > 1 || nestedFieldsOnGenerator.size
== 0) {
+ pushedThrough
+ } else {
+ // 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($"items").as("item")).select($"item.a") =>
+ // df.select(explode($"items.a").as("item.a"))
+ val rewrittenG = newG.transformExpressions {
+ case e: ExplodeBase =>
Review comment:
Ideally it is okay too. We also support other generator pruning through
(plz see `canPruneGenerator`). As the reported case is `explode`, I work on it
first. We can add more support in follow-ups.
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