[GitHub] [spark] minyyy commented on a change in pull request #35850: [SPARK-38529][SQL] Fix a bug that GeneratorNestedColumnAliasing is incorrectly applied to non-Explode generators.

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minyyy commented on a change in pull request #35850:
URL: https://github.com/apache/spark/pull/35850#discussion_r827201964



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
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@@ -321,6 +321,40 @@ object GeneratorNestedColumnAliasing {
     // need to prune nested columns through Project and under Generate. The difference is
     // when `nestedSchemaPruningEnabled` is on, nested columns will be pruned further at
     // file format readers if it is supported.
+
+    // There are [[ExtractValue]] expressions on or not on the output of the generator. Generator
+    // can also have different types:
+    // 1. For [[ExtractValue]]s not on the output of the generator, theoretically speaking, there
+    //    lots of expressions that we can push down, including non ExtractValues and GetArrayItem
+    //    and GetMapValue. But to be safe, we only handle GetStructField and GetArrayStructFields.

Review comment:
       That's the next fix I will make. It is true that we don't limit ExtractValue types but it is incorrect. You can think about Explode and GetArrayItem, GetMapValue, GetArrayStructFields, none of the 3 expressions can be pushed down. 




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