[GitHub] [spark] cloud-fan commented on a change in pull request #28326: [SPARK-27340][SS] Alias on TimeWindow expression cause watermark metadata lost
cloud-fan commented on a change in pull request #28326:
URL: https://github.com/apache/spark/pull/28326#discussion_r415859659
##
File path: sql/core/src/main/scala/org/apache/spark/sql/Column.scala
##
@@ -1040,17 +1034,11 @@ 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 {
-normalizedExpr() match {
- case ne: NamedExpression => Alias(expr, alias)(explicitMetadata =
Some(ne.metadata))
Review comment:
This was added by https://github.com/apache/spark/pull/8215. But looking
at the added tests at that time, we just want to carry over the metadata from
the child of `Alias`, which doesn't need this change as `Alias.metedata` can
inherit its child's metadata.
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[GitHub] [spark] cloud-fan commented on a change in pull request #28326: [SPARK-27340][SS] Alias on TimeWindow expression cause watermark metadata lost
cloud-fan commented on a change in pull request #28326:
URL: https://github.com/apache/spark/pull/28326#discussion_r415531970
##
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
##
@@ -3262,10 +3262,21 @@ object CleanupAliases extends Rule[LogicalPlan] {
def trimNonTopLevelAliases(e: Expression): Expression = e match {
case a: Alias =>
- a.copy(child = trimAliases(a.child))(
+ val newChild = trimAliases(a.child)
+ // Specific logic for keeping the eventTime watermark metadata in the
top level alias.
Review comment:
can we make it general? I think what we need to do is to propagate the
alias metadata when there are contiguous Alias nodes and we merge them into one.
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