[GitHub] [spark] cloud-fan commented on a diff in pull request #40321: [SPARK-42704] SubqueryAlias propagates metadata columns that child outputs

["cloud-fan (via GitHub)" <gi...@apache.org>]

cloud-fan commented on code in PR #40321:
URL: https://github.com/apache/spark/pull/40321#discussion_r1131869082


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala:
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@@ -1033,9 +1033,12 @@ class Analyzer(override val catalogManager: CatalogManager) extends RuleExecutor
         requiredAttrIds.contains(a.exprId)) =>
         s.withMetadataColumns()
       case p: Project if p.metadataOutput.exists(a => requiredAttrIds.contains(a.exprId)) =>
+        // Inject the requested metadata columns into the project's output, if not already present.

Review Comment:
   do we hit a real issue with this? If the metadata col is already in the output, this code path should not be triggered as we have `val metaCols = getMetadataAttributes(node).filterNot(inputAttrs.contains)`
   
   What we can improve is to only include metadata columns that are included in `requiredAttrIds`.



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