Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/12719#discussion_r62805230
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -618,6 +619,48 @@ object NullPropagation extends Rule[LogicalPlan] {
}
/**
+ * Propagate foldable expressions:
+ * Replace attributes with aliases of the original foldable expressions if
possible.
+ * 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] {
+ 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 {
+ val foldableMap =
AttributeMap(foldableExprSet.toSeq.map(_.asInstanceOf[Alias])
+ .map(a => (a.toAttribute, a.child)))
--- End diff --
Yep. That was indeed initial attempts considering various corner cases (Not
exhaustive.)
The key problem was some plans needs 'NamedExpression'. So, if we replace
with literals, it fails at runtime.
Also, `Filter` and `Aggregate.groupingExpression` needs expressions without
names vise versa.
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