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https://issues.apache.org/jira/browse/SPARK-23666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16396832#comment-16396832
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Daniel Darabos commented on SPARK-23666:
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I've looked at the code and both {{ScalaUDF.scala}} and
{{mathExpressions.scala}} just call {{toString}} on an {{Expression}} child. I
don't see why the ID is added in one case and not the other...
> Undeterministic column name with UDFs
> -------------------------------------
>
> Key: SPARK-23666
> URL: https://issues.apache.org/jira/browse/SPARK-23666
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.2.0, 2.3.0
> Reporter: Daniel Darabos
> Priority: Minor
>
> When you access structure fields in Spark SQL, the auto-generated result
> column name includes an internal ID.
> {code:java}
> scala> import spark.implicits._
> scala> Seq(((1, 2), 3)).toDF("a", "b").createOrReplaceTempView("x")
> scala> spark.udf.register("f", (a: Int) => a)
> scala> spark.sql("select f(a._1) from x").show
> +---------------------+
> |UDF:f(a._1 AS _1#148)|
> +---------------------+
> | 1|
> +---------------------+
> {code}
> This ID ({{#148}}) is only included for UDFs.
> {code:java}
> scala> spark.sql("select factorial(a._1) from x").show
> +-----------------------+
> |factorial(a._1 AS `_1`)|
> +-----------------------+
> | 1|
> +-----------------------+
> {code}
> The internal ID is different on every invocation. The problem this causes for
> us is that the schema of the SQL output is never the same:
> {code:java}
> scala> spark.sql("select f(a._1) from x").schema ==
> spark.sql("select f(a._1) from x").schema
> Boolean = false
> {code}
> We rely on similar schema checks when reloading persisted data.
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