cloud-fan commented on a change in pull request #34504:
URL: https://github.com/apache/spark/pull/34504#discussion_r755214307



##########
File path: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -1548,6 +1548,31 @@ object PushPredicateThroughNonJoin extends 
Rule[LogicalPlan] with PredicateHelpe
         filter
       }
 
+    case filter @ Filter(condition, w: Window) if w.partitionSpec.isEmpty =>
+      w.windowExpressions match {
+        case Seq(alias @ Alias(WindowExpression(_: RowNumber, 
WindowSpecDefinition(Nil, orderSpec,
+            SpecifiedWindowFrame(RowFrame, UnboundedPreceding, CurrentRow))), 
_)) =>
+          val aliasAttr = alias.toAttribute
+          val limitValue = splitConjunctivePredicates(condition).collectFirst {
+            case LessThanOrEqual(e, IntegerLiteral(v)) if 
e.semanticEquals(aliasAttr) => v
+            case Equality(e, IntegerLiteral(v)) if e.semanticEquals(aliasAttr) 
=> v
+            case LessThan(e, IntegerLiteral(v)) if e.semanticEquals(aliasAttr) 
=> v - 1
+          }
+
+          limitValue match {
+            case Some(lv) if lv <= 0 =>
+              LocalRelation(filter.output, data = Seq.empty, isStreaming = 
filter.isStreaming)
+            case Some(lv)
+                if lv < conf.topKSortFallbackThreshold && 
w.child.maxRows.forall(_ > lv) =>
+              filter.copy(child =
+                w.copy(child = Limit(Literal(lv), Sort(orderSpec, true, 
w.child))))

Review comment:
       BTW, is `orderSpec` always specified?




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