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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