beliefer commented on a change in pull request #28685:
URL: https://github.com/apache/spark/pull/28685#discussion_r470377487
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
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@@ -474,6 +479,55 @@ 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
Review comment:
``offset`th row of the window` ?
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