Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/2501#discussion_r18081221
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
---
@@ -73,6 +74,52 @@ abstract class LogicalPlan extends
QueryPlan[LogicalPlan] with Logging {
def childrenResolved: Boolean = !children.exists(!_.resolved)
/**
+ * Returns true when the given logical plan will return the same results
as this logical plan.
+ *
+ * Since its likely undecideable 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.
Logical operators that
+ * can do better should override this function.
+ */
+ def sameResult(plan: LogicalPlan): Boolean = {
+ if (plan.children.size != children.size) {
+ false
+ } else if (plan.children.zip(children).exists { case (l, r) =>
!l.sameResult(r) }) {
+ false
+ } else if (plan.getClass != this.getClass) {
+ false
+ } else {
+ logDebug(
+ s"[${cleanArgs.mkString(", ")}] == [${plan.cleanArgs.mkString(",
")}]")
+ cleanArgs == plan.cleanArgs
+ }
+ }
--- End diff --
Moving class and size comparison first would be more efficient:
```scala
plan.getClass == this.getClass &&
plan.children.size == children.size && {
logDebug(s"[${cleanArgs.mkString(", ")}] ==
[${plan.cleanArgs.mkString(", ")}]")
cleanArgs == plan.cleanArgs
} &&
(plan.children, children).zipped.forall(_ sameResult _)
```
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