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https://issues.apache.org/jira/browse/SPARK-18874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16554431#comment-16554431
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Apache Spark commented on SPARK-18874:
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User 'wangyum' has created a pull request for this issue:
https://github.com/apache/spark/pull/21863
> First phase: Deferring the correlated predicate pull up to Optimizer phase
> --------------------------------------------------------------------------
>
> Key: SPARK-18874
> URL: https://issues.apache.org/jira/browse/SPARK-18874
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Reporter: Nattavut Sutyanyong
> Assignee: Dilip Biswal
> Priority: Major
> Fix For: 2.2.0
>
> Attachments: SPARK-18874-3.pdf
>
>
> This JIRA implements the first phase of SPARK-18455 by deferring the
> correlated predicate pull up from Analyzer to Optimizer. The goal is to
> preserve the current functionality of subquery in Spark 2.0 (if it works, it
> continues to work after this JIRA, if it does not, it won't). The performance
> of subquery processing is expected to be at par with Spark 2.0.
> The representation of the LogicalPlan after Analyzer will be different after
> this JIRA that it will preserve the original positions of correlated
> predicates in a subquery. This new representation is a preparation work for
> the second phase of extending the support of correlated subquery to cases
> Spark 2.0 does not support such as deep correlation, outer references in
> SELECT clause.
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