Github user yhuai commented on a diff in the pull request: https://github.com/apache/spark/pull/9819#discussion_r47453065 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala --- @@ -246,85 +260,238 @@ object SpecifiedWindowFrame { } } +case class UnresolvedWindowExpression( + child: Expression, + windowSpec: WindowSpecReference) extends UnaryExpression with Unevaluable { + + override def dataType: DataType = throw new UnresolvedException(this, "dataType") + override def foldable: Boolean = throw new UnresolvedException(this, "foldable") + override def nullable: Boolean = throw new UnresolvedException(this, "nullable") + override lazy val resolved = false +} + +case class WindowExpression( + windowFunction: Expression, + windowSpec: WindowSpecDefinition) extends Expression with Unevaluable { + + override def children: Seq[Expression] = windowFunction :: windowSpec :: Nil + + override def dataType: DataType = windowFunction.dataType + override def foldable: Boolean = windowFunction.foldable + override def nullable: Boolean = windowFunction.nullable + + override def toString: String = s"$windowFunction $windowSpec" +} + /** - * Every window function needs to maintain a output buffer for its output. - * It should expect that for a n-row window frame, it will be called n times - * to retrieve value corresponding with these n rows. + * A window function is a function that can only be evaluated in the context of a window operator. */ trait WindowFunction extends Expression { - def init(): Unit + /** Frame in which the window operator must be executed. */ + def frame: WindowFrame = UnspecifiedFrame --- End diff -- Actually, is it used as the default frame?
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