xuanyuanking commented on a change in pull request #28830:
URL: https://github.com/apache/spark/pull/28830#discussion_r439959045



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File path: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
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@@ -2541,7 +2541,9 @@ class Dataset[T] private[sql](
   def dropDuplicates(colNames: Seq[String]): Dataset[T] = withTypedPlan {
     val resolver = sparkSession.sessionState.analyzer.resolver
     val allColumns = queryExecution.analyzed.output
-    val groupCols = colNames.distinct.flatMap { (colName: String) =>
+    // SPARK-31990: We must keep `toSet.toSeq` here because of the backward 
compatibility issue
+    // (the Streaming's state store depends on the `groupCols` order).
+    val groupCols = colNames.toSet.toSeq.flatMap { (colName: String) =>

Review comment:
       Yep, I also mentioned this at 
https://github.com/apache/spark/pull/28830#discussion_r439909489, we can relay 
on the validation checking and integrated tests.




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