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https://issues.apache.org/jira/browse/SPARK-11111?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Patrick Wendell updated SPARK-11111:
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Component/s: SQL
> Fast null-safe join
> -------------------
>
> Key: SPARK-11111
> URL: https://issues.apache.org/jira/browse/SPARK-11111
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> 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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