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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2015/10/14 22:17:05 UTC
[jira] [Assigned] (SPARK-11111) Fast null-safe join
[ https://issues.apache.org/jira/browse/SPARK-11111?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-11111:
------------------------------------
Assignee: Apache Spark (was: Davies Liu)
> 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: Apache Spark
>
> 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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