[GitHub] [spark] cloud-fan commented on a change in pull request #34580: [SPARK-37270][SQL] Fix push foldable into CaseWhen branches if elseValue is empty

[GitBox <gi...@apache.org>]

cloud-fan commented on a change in pull request #34580:
URL: https://github.com/apache/spark/pull/34580#discussion_r749077669



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -681,7 +681,9 @@ object PushFoldableIntoBranches extends Rule[LogicalPlan] with PredicateHelper {
           if supportedUnaryExpression(u) && atMostOneUnfoldable(branches.map(_._2) ++ elseValue) =>
         c.copy(
           branches.map(e => e.copy(_2 = u.withNewChildren(Array(e._2)))),
-          elseValue.map(e => u.withNewChildren(Array(e))))
+          elseValue
+            .orElse { if (u.isInstanceOf[IsNull]) Some(Literal(null, c.dataType)) else None }

Review comment:
       Can we optimize away the useless else branch? I think null propagation + removing null else branch should do the work?




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