[GitHub] [spark] dongjoon-hyun commented on a change in pull request #24599: [SPARK-27701][SQL] Extend NestedColumnAliasing to more nested field cases

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dongjoon-hyun commented on a change in pull request #24599: [SPARK-27701][SQL] Extend NestedColumnAliasing to more nested field cases
URL: https://github.com/apache/spark/pull/24599#discussion_r291844027
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
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 @@ -86,32 +86,39 @@ object NestedColumnAliasing {
   }
 
   /**
-   * Return root references that are individually accessed as a whole, and `GetStructField`s.
+   * Return root references that are individually accessed as a whole, and `GetStructField`s
+   * or `GetArrayStructField`s which on top of other `ExtractValue`s or special expressions.
+   * Check `SelectedField` to see which expressions should be listed here.
    */
-  private def collectRootReferenceAndGetStructField(e: Expression): Seq[Expression] = e match {
-    case _: AttributeReference | _: GetStructField => Seq(e)
-    case es if es.children.nonEmpty => es.children.flatMap(collectRootReferenceAndGetStructField)
+  private def collectRootReferenceAndExtractValue(e: Expression): Seq[Expression] = e match {
+    case _: AttributeReference |
+         GetStructField(_: ExtractValue | _: AttributeReference, _, _) |
+         GetArrayStructFields(_: MapValues |
+                              _: MapKeys |
+                              _: ExtractValue |
+                              _: AttributeReference, _, _, _, _) => Seq(e)
 
 Review comment:
   Ur, could you split into multiple `case`?

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