Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/11635#discussion_r60440111
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -958,6 +958,26 @@ object PushDownPredicate extends Rule[LogicalPlan]
with PredicateHelper {
project.copy(child = Filter(replaceAlias(condition, aliasMap),
grandChild))
+ // Push [[Filter]] operators through [[Window]] operators. Parts of
the predicate that can be
+ // pushed beneath must satisfy three conditions:
+ // 1. involving one and only one column that is part of window
partitioning key.
+ // 2. Window partitioning key should be just a sequence of
[[AttributeReference]].
--- End diff --
@gatorsmile this restriction is probably more related to the fact that if
we push down an entire expression, e.g.: `a + b`, we also need a place to
evaluate the expression. Which would mean that we have to plan both a Project
and a Filter.
I am pretty sure that we move all expressions used in Window clauses into
an underlying Project during Analysis. So this shouldn't be to big of a problem.
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