beliefer commented on a change in pull request #30387:
URL: https://github.com/apache/spark/pull/30387#discussion_r530151304
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File path: sql/core/src/main/scala/org/apache/spark/sql/functions.scala
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@@ -938,8 +938,40 @@ object functions {
* @group window_funcs
* @since 1.4.0
*/
- def lag(e: Column, offset: Int, defaultValue: Any): Column = withExpr {
- Lag(e.expr, Literal(offset), Literal(defaultValue))
+ def lag(e: Column, offset: Int, defaultValue: Any): Column = {
+ lag(e, offset, defaultValue, false)
+ }
+
+ /**
+ * Window function: returns the value that is `offset` rows before the
current row, and
+ * `defaultValue` if there is less than `offset` rows before the current
row. `ignoreNulls`
+ * determines whether null values of row are included in or eliminated from
the calculation.
+ * For example, an `offset` of one will return the previous row at any given
point in the
+ * window partition.
+ *
+ * This is equivalent to the LAG function in SQL.
+ *
+ * @group window_funcs
+ * @since 3.1.0
+ */
+ def lag(columnName: String, offset: Int, defaultValue: Any, ignoreNulls:
Boolean): Column = {
Review comment:
cc @HyukjinKwon too.
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