cloud-fan commented on code in PR #54236:
URL: https://github.com/apache/spark/pull/54236#discussion_r2817032750
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/SequentialUnionAnalysis.scala:
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@@ -23,8 +23,12 @@ import org.apache.spark.sql.catalyst.trees.TreePattern._
import org.apache.spark.sql.errors.QueryCompilationErrors
/**
- * Flattens nested SequentialStreamingUnion nodes into a single level.
+ * Flattens directly nested SequentialStreamingUnion nodes into a single level.
* This allows chaining: df1.followedBy(df2).followedBy(df3)
+ *
+ * Note: This only handles direct nesting where a SequentialStreamingUnion is
an immediate child.
+ * Nesting wrapped in other operators (e.g.,
Project(SequentialStreamingUnion(...))) is handled
+ * by the optimizer's CombineUnions rule.
*/
object FlattenSequentialStreamingUnion extends Rule[LogicalPlan] {
Review Comment:
not related to this PR, but do we still need this rule? `CombineUnions` can
cover it.
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