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https://issues.apache.org/jira/browse/SPARK-11072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15850985#comment-15850985
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Wenchen Fan commented on SPARK-11072:
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sorry this is stale, let me close it
> simplify self join handling
> ---------------------------
>
> Key: SPARK-11072
> URL: https://issues.apache.org/jira/browse/SPARK-11072
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Wenchen Fan
>
> self-join is a diamond problem that confuse our analyzer. Our current
> solution is creating new instances of leaf nodes in the right tree of join
> node, and update all attribute reference there. Thus there is no diamond
> anymore and problem fixed.
> However, our execution engine can handle diamond plan and we only need to
> distinguish the output between left and right. So we can simplify the
> self-join handling by introducing a new Plan `NewOutput` to give different
> output attributes.
> The extra `NewOutput` layer is quite cheap and can be completely removed when
> we have local nodes.
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