[GitHub] [spark] beliefer commented on a change in pull request #28685: [SPARK-27951][SQL] Support ANSI SQL NTH_VALUE window function

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

beliefer commented on a change in pull request #28685:
URL: https://github.com/apache/spark/pull/28685#discussion_r469670262



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/windowExpressions.scala
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@@ -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

Review comment:
       OK




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