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https://issues.apache.org/jira/browse/SPARK-28225?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Leverentz resolved SPARK-28225.
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Resolution: Not A Problem
> Unexpected behavior for Window functions
> ----------------------------------------
>
> Key: SPARK-28225
> URL: https://issues.apache.org/jira/browse/SPARK-28225
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.4.0
> Reporter: Andrew Leverentz
> Priority: Major
>
> I've noticed some odd behavior when combining the "first" aggregate function
> with an ordered Window.
> In particular, I'm working with columns created using the syntax
> {code}
> first($"y", ignoreNulls = true).over(Window.orderBy($"x"))
> {code}
> Below, I'm including some code which reproduces this issue in a Databricks
> notebook.
> *Code:*
> {code:java}
> import org.apache.spark.sql.functions.first
> import org.apache.spark.sql.expressions.Window
> import org.apache.spark.sql.Row
> import org.apache.spark.sql.types.{StructType,StructField,IntegerType}
> val schema = StructType(Seq(
> StructField("x", IntegerType, false),
> StructField("y", IntegerType, true),
> StructField("z", IntegerType, true)
> ))
> val input =
> spark.createDataFrame(sc.parallelize(Seq(
> Row(101, null, 11),
> Row(102, null, 12),
> Row(103, null, 13),
> Row(203, 24, null),
> Row(201, 26, null),
> Row(202, 25, null)
> )), schema = schema)
> input.show
> val output = input
> .withColumn("u1", first($"y", ignoreNulls =
> true).over(Window.orderBy($"x".asc_nulls_last)))
> .withColumn("u2", first($"y", ignoreNulls =
> true).over(Window.orderBy($"x".asc)))
> .withColumn("u3", first($"y", ignoreNulls =
> true).over(Window.orderBy($"x".desc_nulls_last)))
> .withColumn("u4", first($"y", ignoreNulls =
> true).over(Window.orderBy($"x".desc)))
> .withColumn("u5", first($"z", ignoreNulls =
> true).over(Window.orderBy($"x".asc_nulls_last)))
> .withColumn("u6", first($"z", ignoreNulls =
> true).over(Window.orderBy($"x".asc)))
> .withColumn("u7", first($"z", ignoreNulls =
> true).over(Window.orderBy($"x".desc_nulls_last)))
> .withColumn("u8", first($"z", ignoreNulls =
> true).over(Window.orderBy($"x".desc)))
> output.show
> {code}
> *Expectation:*
> Based on my understanding of how ordered-Window and aggregate functions work,
> the results I expected to see were:
> * u1 = u2 = constant value of 26
> * u3 = u4 = constant value of 24
> * u5 = u6 = constant value of 11
> * u7 = u8 = constant value of 13
> However, columns u1, u2, u7, and u8 contain some unexpected nulls.
> *Results:*
> {code:java}
> +---+----+----+----+----+---+---+---+---+----+----+
> | x| y| z| u1| u2| u3| u4| u5| u6| u7| u8|
> +---+----+----+----+----+---+---+---+---+----+----+
> |203| 24|null| 26| 26| 24| 24| 11| 11|null|null|
> |202| 25|null| 26| 26| 24| 24| 11| 11|null|null|
> |201| 26|null| 26| 26| 24| 24| 11| 11|null|null|
> |103|null| 13|null|null| 24| 24| 11| 11| 13| 13|
> |102|null| 12|null|null| 24| 24| 11| 11| 13| 13|
> |101|null| 11|null|null| 24| 24| 11| 11| 13| 13|
> +---+----+----+----+----+---+---+---+---+----+----+
> {code}
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