Github user fhueske commented on a diff in the pull request: https://github.com/apache/flink/pull/4471#discussion_r132230387 --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/util/UpdatingPlanChecker.scala --- @@ -56,17 +59,20 @@ object UpdatingPlanChecker { } /** Identifies unique key fields in the output of a RelNode. */ - private class UniqueKeyExtractor extends RelVisitor { - - var keys: Option[Array[String]] = None + private class UniqueKeyExtractor { - override def visit(node: RelNode, ordinal: Int, parent: RelNode): Unit = { + // visit() function will return a tuple, the first element of tuple is the key, the second is + // the key's corresponding ancestor. Ancestors are used to identify same keys, for example: + // select('pk as pk1, 'pk as pk2), both pk1 and pk2 have the same ancestor, i.e., pk. + // A node having keys means: 1.it generates keys by itself 2.all ancestors from it's upstream + // nodes have been preserved even though the ancestors have been duplicated. + def visit(node: RelNode): Option[List[(String, String)]] = { node match { case c: DataStreamCalc => - super.visit(node, ordinal, parent) - // check if input has keys - if (keys.isDefined) { - // track keys forward + val keyAncestors = visit(node.getInput(0)) --- End diff -- `keyAncestors` -> `inputKeys`?
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