Github user nsyca commented on a diff in the pull request:
https://github.com/apache/spark/pull/17520#discussion_r109522050
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -792,6 +824,39 @@ object PushDownPredicate extends Rule[LogicalPlan]
with PredicateHelper {
filter
}
+ // Similar to the above Filter over Window
+ // LeftSemi/LeftAnti over Window
+ case join @ Join(w: Window, rightOp, LeftSemiOrAnti(joinType),
joinCond)
+ if w.partitionSpec.forall(_.isInstanceOf[AttributeReference]) =>
+ if (joinCond.isEmpty) {
+ // No join condition, just push down Join below Window
+ w.copy(child = Join(w.child, rightOp, joinType, joinCond))
+ } else {
+ val partitionAttrs =
AttributeSet(w.partitionSpec.flatMap(_.references)) ++
+ rightOp.outputSet
+
+ val (candidates, containingNonDeterministic) =
+ splitConjunctivePredicates(joinCond.get).span(_.deterministic)
+
+ val (pushDown, rest) = candidates.partition { cond =>
+ cond.references.subsetOf(partitionAttrs) &&
+ !SubqueryExpression.hasCorrelatedSubquery(cond) &&
+ !SubExprUtils.containsOuter(cond)
+ }
+
+ val stayUp = rest ++ containingNonDeterministic
+
+ if (pushDown.nonEmpty) {
+ val pushDownPredicate = pushDown.reduce(And)
+ val newPlan = w.copy(child = Join(w.child, rightOp, joinType,
Option(pushDownPredicate)))
+ if (stayUp.isEmpty) newPlan else Filter(stayUp.reduce(And),
newPlan)
+ } else {
+ // The join condition is not a subset of the Window's PARTITION
BY clause,
+ // no push down.
+ join
+ }
+ }
+
--- End diff --
Unlike the cases of Aggregate and Union (see the comments below), Window
never reduces the cardinality of the input stream, hence pushing down the
LeftSemi/LeftAnti join (which guarantees by their semantics that it never
expands the cardinality of their parent table) is safer.
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