[GitHub] [spark] maropu commented on a change in pull request #31402: [SPARK-34296][SQL] AggregateWindowFunction frame should not always use UnboundedPreceding

[GitBox <gi...@apache.org>]

maropu commented on a change in pull request #31402:
URL: https://github.com/apache/spark/pull/31402#discussion_r567518596



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
##########
@@ -633,7 +636,9 @@ case class CumeDist() extends RowNumberLike with SizeBasedWindowFunction {
   group = "window_funcs")
 // scalastyle:on line.size.limit line.contains.tab
 case class NthValue(input: Expression, offset: Expression, ignoreNulls: Boolean)
-    extends AggregateWindowFunction with OffsetWindowFunction with ImplicitCastInputTypes {
+    extends SpecifiedFrameAggregateWindowFunction

Review comment:
       Why we need to extend `SpecifiedFrameAggregateWindowFunction` even though `frame` with `UnspecifiedFrame` is overridden in L649?

##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
##########
@@ -511,14 +511,17 @@ case class Lag(
 
 abstract class AggregateWindowFunction extends DeclarativeAggregate with WindowFunction {
   self: Product =>
-  override val frame: WindowFrame = SpecifiedWindowFrame(RowFrame, UnboundedPreceding, CurrentRow)
   override def dataType: DataType = IntegerType
   override def nullable: Boolean = true
   override lazy val mergeExpressions =
     throw QueryExecutionErrors.mergeUnsupportedByWindowFunctionError
 }
 
-abstract class RowNumberLike extends AggregateWindowFunction {
+abstract class SpecifiedFrameAggregateWindowFunction extends AggregateWindowFunction {
+  override val frame: WindowFrame = SpecifiedWindowFrame(RowFrame, UnboundedPreceding, CurrentRow)
+}
+
+abstract class RowNumberLike extends SpecifiedFrameAggregateWindowFunction {

Review comment:
       Why we can still use `UnboundedPreceding` for row number-like window funcs?




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