beliefer commented on a change in pull request #28685:
URL: https://github.com/apache/spark/pull/28685#discussion_r476096152
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
##########
@@ -474,6 +480,54 @@ case class Lag(input: Expression, offset: Expression,
default: Expression)
override val direction = Descending
}
+/**
+ * The NthValue function returns the value of `input` at the `offset`th row
from beginning of the
+ * window frame. Offsets start at 1. 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
+ from beginning of the window frame. Offsets start at 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 startWithCurrentRow = false
+
+ override val direction = Ascending
+
+ override def checkInputDataTypes(): TypeCheckResult = {
+ val check = super.checkInputDataTypes()
+ if (check.isFailure) {
+ check
+ } else if (offset.foldable) {
+ offset.dataType match {
+ case IntegerType =>
+ offset.eval().asInstanceOf[Int] 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 _ => TypeCheckSuccess
+ }
+ case _ => TypeCheckFailure(
+ s"The 'offset' parameter must be a int literal but it is
${offset.dataType}.")
Review comment:
postgresql: integer
oracle:integer
redshift:integer
vertica:integer
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