xuanyuanking commented on a change in pull request #24457:
[SPARK-27340][Streaming] Alias on TimeWindow expression may cause watermark
metadata lost
URL: https://github.com/apache/spark/pull/24457#discussion_r281443354
##########
File path: sql/core/src/main/scala/org/apache/spark/sql/Column.scala
##########
@@ -1001,17 +1001,11 @@ class Column(val expr: Expression) extends Logging {
* df.select($"colA".name("colB"))
* }}}
*
- * If the current column has metadata associated with it, this metadata will
be propagated
- * to the new column. If this not desired, use `as` with explicitly empty
metadata.
- *
* @group expr_ops
* @since 2.0.0
*/
def name(alias: String): Column = withExpr {
- expr match {
- case ne: NamedExpression => Alias(expr, alias)(explicitMetadata =
Some(ne.metadata))
- case other => Alias(other, alias)()
- }
+ Alias(expr, alias)()
Review comment:
Related tests maybe not enough, as your change, `as` function has a
different behavior, `metadata` no longer pass to `explicitMetadata`. My
suggestion:
1. For safety, run all test, not only the related.
2. Do the fix just for SS scenario.
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