beliefer commented on a change in pull request #28685:
URL: https://github.com/apache/spark/pull/28685#discussion_r469674334
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
##########
@@ -474,6 +479,52 @@ case class Lag(input: Expression, offset: Expression,
default: Expression)
override val direction = Descending
}
+/**
+ * The NthValue function returns the value of `input` at the row that is the
`offset`th row of
+ * the window frame (counting from 1). Offsets start at 0, which is the
current row. When the
+ * value of `input` is null at the `offset`th row or there is no such an
`offset`th row, null
+ * is returned.
+ *
+ * @param input expression to evaluate `offset`th row of the window frame.
+ * @param offset rows to jump ahead in the partition.
+ */
+@ExpressionDescription(
+ usage = """
+ _FUNC_(input[, offset]) - Returns the value of `input` at the row that is
the`offset`th row
+ of the window frame (counting from 1). If the value of `input` at the
`offset`th row is
+ null, null is returned. If there is no such an offset row (e.g., when
the offset is 10,
+ size of the window frame less than 10), null is returned.
+ """,
+ since = "3.1.0")
+case class NthValue(input: Expression, offset: Expression)
+ extends OffsetWindowFunction {
+
+ override val default = Literal(null)
+
+ override val isWholeBased = true
+
+ override val direction = Ascending
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ val check = super.checkInputDataTypes()
+ if (check.isFailure) {
+ check
+ } else if (offset.foldable) {
+ offset.eval() match {
+ case i: Int if i <= 0 => TypeCheckFailure(
+ s"The 'offset' argument of nth_value must be greater than zero but
it is $i.")
+ case i: Int => TypeCheckSuccess
+ case other => TypeCheckFailure(
+ s"The 'offset' parameter must be a int literal but it is $other.")
Review comment:
OK
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