[GitHub] [spark] maropu commented on a change in pull request #24765: [SPARK-27915][SQL][WIP] Update logical Filter's output nullability based on IsNotNull conditions

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maropu commented on a change in pull request #24765: [SPARK-27915][SQL][WIP] Update logical Filter's output nullability based on IsNotNull conditions
URL: https://github.com/apache/spark/pull/24765#discussion_r303719053
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala
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 @@ -51,7 +51,14 @@ case class Subquery(child: LogicalPlan) extends OrderPreservingUnaryNode {
 
 case class Project(projectList: Seq[NamedExpression], child: LogicalPlan)
     extends OrderPreservingUnaryNode {
-  override def output: Seq[Attribute] = projectList.map(_.toAttribute)
+  override def output: Seq[Attribute] = {
+    // The child operator may have inferred more precise nullability information
+    // for the project expression, so leverage that information if it's availble:
+    val childOutputNullability = child.output.map(a => a.exprId -> a.nullable).toMap
+    projectList
+      .map(_.toAttribute)
+      .map{ a => childOutputNullability.get(a.exprId).map(a.withNullability).getOrElse(a) }
 
 Review comment:
   We need to fix this part? It seems `UpdateAttributeNullability` could handle this case if `Filter.output` works well?

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