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Posted to issues@spark.apache.org by "Apache Spark (Jira)" <ji...@apache.org> on 2021/04/07 03:19:00 UTC
[jira] [Commented] (SPARK-34974) Improve the subquery decorrelation
framework
[ https://issues.apache.org/jira/browse/SPARK-34974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17315930#comment-17315930 ]
Apache Spark commented on SPARK-34974:
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User 'allisonwang-db' has created a pull request for this issue:
https://github.com/apache/spark/pull/32072
> Improve the subquery decorrelation framework
> --------------------------------------------
>
> Key: SPARK-34974
> URL: https://issues.apache.org/jira/browse/SPARK-34974
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: Allison Wang
> Priority: Major
>
> Currently, Spark has limited support for correlated subqueries. It only allows Filter to have outer column references and does not support non-equality predicates when the subquery is aggregated. Please see https://issues.apache.org/jira/browse/SPARK-18455 for more details on how subquery decorrelation works in Spark.
> The task here is to implement the technique introduced in "Unnesting Arbitrary Queries" by T. Neumann; A. Kemper
> ([http://www.btw-2015.de/res/proceedings/Hauptband/Wiss/Neumann-Unnesting_Arbitrary_Querie.pdf]). This allows Spark to have outer query column references other than Filter, decorrelate subqueries with more types of operators, and support correlated non-equality predicates.
> This will also enable supporting lateral derived table (https://issues.apache.org/jira/browse/SPARK-34382) in the future.
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