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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (SPARK-11111) Fast null-safe join
Date Wed, 14 Oct 2015 20:17:05 GMT

     [ https://issues.apache.org/jira/browse/SPARK-11111?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Apache Spark reassigned SPARK-11111:
------------------------------------

    Assignee: Davies Liu  (was: Apache Spark)

> Fast null-safe join
> -------------------
>
>                 Key: SPARK-11111
>                 URL: https://issues.apache.org/jira/browse/SPARK-11111
>             Project: Spark
>          Issue Type: Improvement
>            Reporter: Davies Liu
>            Assignee: Davies Liu
>
> Today, null safe joins are executed with a Cartesian product.
> {code}
> scala> sqlContext.sql("select * from t a join t b on (a.i <=> b.i)").explain
> == Physical Plan ==
> TungstenProject [i#2,j#3,i#7,j#8]
>  Filter (i#2 <=> i#7)
>   CartesianProduct
>    LocalTableScan [i#2,j#3], [[1,1]]
>    LocalTableScan [i#7,j#8], [[1,1]]
> {code}
> One option is to add this rewrite to the optimizer:
> {code}
> select * 
> from t a 
> join t b 
>   on coalesce(a.i, <default>) = coalesce(b.i, <default>) AND (a.i <=>
b.i)
> {code}
> Acceptance criteria: joins with only null safe equality should not result in a Cartesian
product.



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