[jira] [Created] (SPARK-20010) Sort information is lost after sort merge join

["Zhenhua Wang (JIRA)" <ji...@apache.org>]

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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