HeartSaVioR commented on a change in pull request #28830:
URL: https://github.com/apache/spark/pull/28830#discussion_r439903851
##########
File path: sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala
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@@ -2548,6 +2548,21 @@ class DataFrameSuite extends QueryTest
assert(df.schema === new StructType().add(StructField("d",
DecimalType(38, 0))))
}
}
+
+ test("SPARK-31990: preserves the input order of colNames in dropDuplicates")
{
+ val df = Seq((1, 2, 3, 4, 5), (1, 2, 3, 4, 5)).toDF("c", "e", "d", "a",
"b")
+ val inputColNames = Seq("c", "b", "c", "d", "b", "c", "b")
Review comment:
You may want to find the case where `toSet.toSeq` produces different
order than `distinct`.
And then you may need to craft a streaming query doing dropDuplicate with
having grouping key just you found, and run the query with Spark 2.4.x (where
SPARK-31292 is not applied), and store checkpoint, and run the query with Spark
3.x (where SPARK-31292 is applied) with restoring checkpoint.
There're a couple of test suites doing that - one of example is
https://github.com/apache/spark/blob/8282bbf12d4e174986a649023ce3984aae7d7755/sql/core/src/test/scala/org/apache/spark/sql/streaming/FlatMapGroupsWithStateSuite.scala#L880-L952
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