viirya commented on a change in pull request #35850:
URL: https://github.com/apache/spark/pull/35850#discussion_r827216842



##########
File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -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:
       We have a check in the rule. For certain generator input, e.g. Map, they 
will not be handled now.




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