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From "Nattavut Sutyanyong (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-16951) Alternative implementation of NOT IN to Anti-join
Date Wed, 21 Dec 2016 19:17:58 GMT

    [ https://issues.apache.org/jira/browse/SPARK-16951?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15767904#comment-15767904
] 

Nattavut Sutyanyong commented on SPARK-16951:
---------------------------------------------

I was wrong on case 3 when the subquery produces empty row. The semantics of the predicate

<expr> NOT IN ( <query-block> )

is

<expr> <> ALL ( <query-block> )

which is when the result of the <query-block> is empty, the predicate is True and therefore
all the rows from the parent side is returned.

> Alternative implementation of NOT IN to Anti-join
> -------------------------------------------------
>
>                 Key: SPARK-16951
>                 URL: https://issues.apache.org/jira/browse/SPARK-16951
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 2.0.0
>            Reporter: Nattavut Sutyanyong
>
> A transformation currently used to process {{NOT IN}} subquery is to rewrite to a form
of Anti-join with null-aware property in the Logical Plan and then translate to a form of
{{OR}} predicate joining the parent side and the subquery side of the {{NOT IN}}. As a result,
the presence of {{OR}} predicate is limited to the nested-loop join execution plan, which
will have a major performance implication if both sides' results are large.
> This JIRA sketches an idea of changing the OR predicate to a form similar to the technique
used in the implementation of the Existence join that addresses the problem of {{EXISTS (..)
OR ..}} type of queries.



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