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https://issues.apache.org/jira/browse/SPARK-22806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16293716#comment-16293716
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Marco Gaido commented on SPARK-22806:
-------------------------------------

This is the right behavior. Also Postgres works like this. if you specify the 
order by clause, by default the range is UNBOUNDED PRECEDING - CURRENT ROW.

> Window Aggregate functions: unexpected result at ordered partition
> ------------------------------------------------------------------
>
>                 Key: SPARK-22806
>                 URL: https://issues.apache.org/jira/browse/SPARK-22806
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Attila Zsolt Piros
>         Attachments: WindowFunctionsWithGroupByError.scala
>
>
> I got different results for aggregate functions (even for sum and count) when 
> the partition is ordered "Window.partitionBy(column).orderBy(column))" and 
> when it is not ordered 'Window.partitionBy(column)".
> Example:
> {code:java}
> test("count, sum, stddev_pop functions over window") {
>     val df = Seq(
>       ("a", 1, 100.0),
>       ("b", 1, 200.0)).toDF("key", "partition", "value")
>     df.createOrReplaceTempView("window_table")
>     checkAnswer(
>       df.select(
>         $"key",
>         count("value").over(Window.partitionBy("partition")),
>         sum("value").over(Window.partitionBy("partition")),
>         stddev_pop("value").over(Window.partitionBy("partition"))
>       ),
>       Seq(
>         Row("a", 2, 300.0, 50.0),
>         Row("b", 2, 300.0, 50.0)))
>   }
>   test("count, sum, stddev_pop functions over ordered by window") {
>     val df = Seq(
>       ("a", 1, 100.0),
>       ("b", 1, 200.0)).toDF("key", "partition", "value")
>     df.createOrReplaceTempView("window_table")
>     checkAnswer(
>       df.select(
>         $"key",
>         count("value").over(Window.partitionBy("partition").orderBy("key")),
>         sum("value").over(Window.partitionBy("partition").orderBy("key")),
>         
> stddev_pop("value").over(Window.partitionBy("partition").orderBy("key"))
>       ),
>       Seq(
>         Row("a", 2, 300.0, 50.0),
>         Row("b", 2, 300.0, 50.0)))
>   }
> {code}
> The "count, sum, stddev_pop functions over ordered by window" fails with the 
> error:
> {noformat}
> == Results ==
> !== Correct Answer - 2 ==   == Spark Answer - 2 ==
> !struct<>                   struct<key:string,count(value) OVER (PARTITION BY 
> partition ORDER BY key ASC NULLS FIRST unspecifiedframe$()):bigint,sum(value) 
> OVER (PARTITION BY partition ORDER BY key ASC NULLS FIRST 
> unspecifiedframe$()):double,stddev_pop(value) OVER (PARTITION BY partition 
> ORDER BY key ASC NULLS FIRST unspecifiedframe$()):double>
> ![a,2,300.0,50.0]           [a,1,100.0,0.0]
>  [b,2,300.0,50.0]           [b,2,300.0,50.0]
> {noformat}
>  



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