Zhenhua Wang created SPARK-20010:
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Summary: Sort information is lost after sort merge join
Key: SPARK-20010
URL: https://issues.apache.org/jira/browse/SPARK-20010
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.2.0
Reporter: Zhenhua Wang
After sort merge join for inner join, now we only keep left key ordering.
However, after inner join, right key has the same value and order as left key.
So if we need another smj on right key, we will unnecessarily add a sort which
causes additional cost.
As a more complicated example, A join B on A.key = B.key join C on B.key =
C.key join D on A.key = D.key. We will unnecessarily add a sort on B.key when
join {AB} and C, and add a sort on A.key when join {ABC} and D.
To fix this, we need to propagate all sorted information (equivalent
expressions) from bottom up.
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