[GitHub] [spark] maropu commented on a change in pull request #24525: [SPARK-27633][SQL] Remove redundant aliases in NestedColumnAliasing

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maropu commented on a change in pull request #24525: [SPARK-27633][SQL] Remove redundant aliases in NestedColumnAliasing
URL: https://github.com/apache/spark/pull/24525#discussion_r315050169
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
 ##########
 @@ -119,9 +119,21 @@ object NestedColumnAliasing {
       .filter(!_.references.subsetOf(AttributeSet(otherRootReferences)))
       .groupBy(_.references.head)
       .flatMap { case (attr, nestedFields: Seq[ExtractValue]) =>
+        // Remove redundant `ExtractValue`s if they share the same parent nest field.
+        // For example, when `a.b` and `a.b.c` are in project list, we only need to alias `a.b`.
+        // We only need to deal with two `ExtractValue`: `GetArrayStructFields` and
+        // `GetStructField`. Please refer to the method `collectRootReferenceAndExtractValue`.
+        val dedupNestedFields = nestedFields.filter {
+          case a @ GetArrayStructFields(child, _, _, _, _) =>
+            nestedFields.forall(f => f == a || child.find(_.semanticEquals(f)).isEmpty)
+          case n @ GetStructField(child, _, _) =>
+            nestedFields.forall(f => f == n || child.find(_.semanticEquals(f)).isEmpty)
 
 Review comment:
   Can we merge the two entry into one? e.g.,
   ```
             case e @ (_: GetStructField | _: GetArrayStructFields) =>
               nestedFields.forall(f => f == e || e.children.head.find(_.semanticEquals(f)).isEmpty)
   ```

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