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https://issues.apache.org/jira/browse/SPARK-17995?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15587348#comment-15587348
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Wenchen Fan commented on SPARK-17995:
-------------------------------------
Can we just add a `newOuterJoinAttrs: Seq[Attribute]` parameter in the `Join`
class? e.g.
{code}
case class Join(..., newOuterJoinAttrs: Seq[Attribute])
object Join {
def apply(...) = {
val newOuterJoinAttrs = joinType match {
case LeftOuterJoin => right.output.map(_.newInstance)
}
}
}
{code}
> Use new attributes for columns from outer joins
> -----------------------------------------------
>
> Key: SPARK-17995
> URL: https://issues.apache.org/jira/browse/SPARK-17995
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 1.6.2, 2.0.0, 2.1.0
> Reporter: Ryan Blue
>
> Plans involving outer joins use the same attribute reference (by exprId) to
> reference columns above the join and below the join. This is a false
> equivalence that leads to bugs like SPARK-16181, in which an attributes were
> incorrectly replaced by the optimizer. The column has a different schema
> above the outer join because its values may be null. The fix for that issue,
> [PR #13884](https://github.com/apache/spark/pull/13884) has a TODO comment
> from [~cloud_fan] to fix this by using different attributes instead of
> needing to special-case outer joins in rules and this issue is to track that
> improvement.
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