beliefer commented on a change in pull request #28685:
URL: https://github.com/apache/spark/pull/28685#discussion_r437999658
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File path: sql/core/src/main/scala/org/apache/spark/sql/functions.scala
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@@ -993,6 +993,30 @@ object functions {
Lead(e.expr, Literal(offset), Literal(defaultValue))
}
+ /**
+ * Window function: returns the value that is the `offset`th row of the
window frame
+ * (counting from 1), and `null` if the size of window frame is less than
`offset` rows.
+ *
+ * This is equivalent to the nth_value function in SQL.
+ *
+ * @group window_funcs
+ * @since 3.0.0
+ */
+ def nth_value(columnName: String, offset: Int): Column = {
Review comment:
They are existing two differences.
The first is:
The offset of `lag` based on the current row in the window.
The offset of `nth_value` based on the first row in the window.
The second is.
The offset of `lag` increases from back to front.
The offset of `nth_value` increases from front to back.
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