cloud-fan commented on a change in pull request #29643:
URL: https://github.com/apache/spark/pull/29643#discussion_r484626924
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala
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@@ -168,6 +170,89 @@ abstract class QueryPlan[PlanType <: QueryPlan[PlanType]]
extends TreeNode[PlanT
}.toSeq
}
+ /**
+ * A variant of `transformUp`, which takes care of the case that the rule
replaces a plan node
+ * with a new one that has different output expr IDs, by updating the
attribute references in
+ * the parent nodes accordingly.
+ *
+ * @param rule the function to transform plan nodes, and return new nodes
with attributes mapping
Review comment:
Because that's too hard. For example, `WidenSetOperationTypes` returns
attribute mapping according to the replaced children, not itself, because
itself may not be resolved yet. While for self-join dedup, we return attribute
mapping according to the current node.
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