Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/11403#discussion_r55453277
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala
---
@@ -237,4 +237,65 @@ abstract class QueryPlan[PlanType <:
TreeNode[PlanType]] extends TreeNode[PlanTy
}
override def innerChildren: Seq[PlanType] = subqueries
+
+ /**
+ * Canonicalized copy of this query plan.
+ */
+ protected lazy val canonicalized: PlanType = this
+
+ /**
+ * Returns true when the given query plan will return the same results
as this query plan.
+ *
+ * Since its likely undecidable to generally determine if two given
plans will produce the same
+ * results, it is okay for this function to return false, even if the
results are actually
+ * the same. Such behavior will not affect correctness, only the
application of performance
+ * enhancements like caching. However, it is not acceptable to return
true if the results could
+ * possibly be different.
+ *
+ * By default this function performs a modified version of equality that
is tolerant of cosmetic
+ * differences like attribute naming and or expression id differences.
Operators that
+ * can do better should override this function.
+ */
+ def sameResult(plan: PlanType): Boolean = {
+ val cleanLeft = this.canonicalized
--- End diff --
Should this be renamed to `canonicalizedLeft`?
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