[jira] [Created] (SPARK-11111) Fast null-safe join

["Davies Liu (JIRA)" <ji...@apache.org>]

Davies Liu created SPARK-11111:
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             Summary: 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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