Github user JoshRosen commented on a diff in the pull request: https://github.com/apache/spark/pull/11403#discussion_r55453264 --- 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 + + /** + * Cleaned copy of this query plan. + */ + protected lazy val cleaned: 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.cleaned + val cleanRight = plan.cleaned + cleanLeft.getClass == cleanRight.getClass && + cleanLeft.children.size == cleanRight.children.size && + cleanLeft.cleanArgs == cleanRight.cleanArgs && + (cleanLeft.children, cleanRight.children).zipped.forall(_ sameResult _) + } + + /** + * All the attributes that are used for this plan. + */ + lazy val allAttributes: Seq[Attribute] = children.flatMap(_.output) + + private def cleanExpression(e: Expression): Expression = e match { --- End diff -- Should this be named to `canonicalizeExpression` in light of the `cleaned` -> `canonicalized` renaming above?
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