[jira] [Commented] (SPARK-18455) General support for subquery processing

["Nattavut Sutyanyong (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-18455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15668521#comment-15668521 ] 

Nattavut Sutyanyong commented on SPARK-18455:
---------------------------------------------

Two papers were discussed as possible solutions for this work.

[1]
"Complex query decorrelation", 
P. Seshadri; H. Pirahesh; T. Y. C. Leung
Data Engineering, 1996. Proceedings of the Twelfth International Conference on
Year: 1996 Pages: 450 - 458
IEEE Conference Publications
[2]
"Unnesting Arbitrary Queries"
T. Neumann; A. Kemper
2015
(http://www.btw-2015.de/res/proceedings/Hauptband/Wiss/Neumann-Unnesting_Arbitrary_Querie.pdf)

In summary, those two papers describe a very similar algorithm to transform correlated subquery to non-correlation subquery.

> General support for subquery processing
> ---------------------------------------
>
>                 Key: SPARK-18455
>                 URL: https://issues.apache.org/jira/browse/SPARK-18455
>             Project: Spark
>          Issue Type: Story
>          Components: SQL
>            Reporter: Nattavut Sutyanyong
>
> Subquery was introduced to Spark in 2.0. With the support of the Subquery, a few queries in the TPC benchmarks are able to run without any syntax error. However, a number of limitations are also enforced in the feature. This JIRA is opened to track the progress of lifting those limitations in processing Subquery.



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