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https://issues.apache.org/jira/browse/SPARK-23439?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16367414#comment-16367414
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Wenchen Fan commented on SPARK-23439:
-------------------------------------
This is a valid behavior, as `a.b` is an invalid column name for most of the
external storages like parquet. I think it's reasonable to name the nested file
according to the deepest field. Users should manually alias the column to avoid
duplication before saving data to external storages.
> Ambiguous reference when selecting column inside StructType with same name
> that outer colum
> -------------------------------------------------------------------------------------------
>
> Key: SPARK-23439
> URL: https://issues.apache.org/jira/browse/SPARK-23439
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.2.0
> Environment: Scala 2.11.8, Spark 2.2.0
> Reporter: Alejandro Trujillo Caballero
> Priority: Minor
>
> Hi.
> I've seen that when working with nested struct fields in a DataFrame and
> doing a select operation the nesting is lost and this can result in
> collisions between column names.
> For example:
>
> {code:java}
> case class Foo(a: Int, b: Bar)
> case class Bar(a: Int)
> val items = List(
> Foo(1, Bar(1)),
> Foo(2, Bar(2))
> )
> val df = spark.createDataFrame(items)
> val df_a_a = df.select($"a", $"b.a").show
> //+---+---+
> //| a| a|
> //+---+---+
> //| 1| 1|
> //| 2| 2|
> //+---+---+
> df.select($"a", $"b.a").printSchema
> //root
> //|-- a: integer (nullable = false)
> //|-- a: integer (nullable = true)
> df.select($"a", $"b.a").select($"a")
> //org.apache.spark.sql.AnalysisException: Reference 'a' is ambiguous, could
> be: a#9, a#{code}
>
>
> Shouldn't the second column be named "b.a"?
>
> Thanks.
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