Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/12719#discussion_r62786561
--- 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 --
this has a really complex process flow, and hard to verify its correctness,
we can simplify it to:
1. find one project that contains foldable project list.
2. build an attribute map of foldable expression
3. transformUp the plan tree, replace the attribute with corresponding
foldable expression, and stop the transformation when meeting `Command` or
`Union`. e.g. you can use a boolean variable to indicate we should stop or not.
4. clean up aliases
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
