Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/12719#discussion_r62787780
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -618,6 +619,52 @@ object NullPropagation extends Rule[LogicalPlan] {
}
/**
+ * Propagate foldable expressions:
+ * Replace all attributes with aliases of the original foldable
expressions except Union queries.
+ * Aliases and ordinal expressions are the main target to be transformed
after propagation. Other
+ * optimizations will take advantage of the propagated foldable
expressions.
+ *
+ * {{{
+ * SELECT 1.0 x, 'abc' y, Now() z ORDER BY x, y, 3
+ * ==> SELECT 1.0 x, 'abc' y, Now() z ORDER BY 1.0, 'abc', Now()
+ * }}}
+ */
+object FoldablePropagation extends Rule[LogicalPlan] {
+ private def hasCommandOrUnion(plan: LogicalPlan): Boolean = plan.find {
+ case _: Command => true
+ case _: Union => true
+ case _ => false
+ }.isDefined
+
+ private def replaceInSubplan(plan: LogicalPlan): LogicalPlan =
plan.transformUp {
+ case subplan: LogicalPlan if !hasCommandOrUnion(subplan) =>
this(subplan)
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = {
+ val foldableExprSet = ExpressionSet(plan.flatMap {
+ case Project(projectList, _) => projectList.collect {
+ case a: Alias if a.resolved && a.child.foldable => a
+ }
+ case _ => Nil
+ })
+
+ if (foldableExprSet.isEmpty) {
+ plan
+ } else if (hasCommandOrUnion(plan)) {
+ replaceInSubplan(plan)
--- End diff --
Do you mean changing all the current optimizer logic or only
`replaceInSubplan`?
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