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https://issues.apache.org/jira/browse/SPARK-12613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15080665#comment-15080665
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Apache Spark commented on SPARK-12613:
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User 'gatorsmile' has created a pull request for this issue:
https://github.com/apache/spark/pull/10566
> Elimination of Outer Join by Parent Join Condition
> --------------------------------------------------
>
> Key: SPARK-12613
> URL: https://issues.apache.org/jira/browse/SPARK-12613
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 1.6.0
> Reporter: Xiao Li
> Priority: Critical
>
> Given an outer join is involved in another join (called parent join), when
> the join type of the parent join is inner, left-semi, left-outer and
> right-outer, checking if the join condition of the parent join satisfies the
> following two conditions:
> 1) there exist null filtering predicates against the columns in the
> null-supplying side of parent join.
> 2) these columns are from the child join.
> If having such join predicates, execute the elimination rules:
> - full outer -> inner if both sides of the child join have such predicates
> - left outer -> inner if the right side of the child join has such predicates
> - right outer -> inner if the left side of the child join has such predicates
> - full outer -> left outer if only the left side of the child join has such
> predicates
> - full outer -> right outer if only the right side of the child join has
> such predicates
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