[jira] [Created] (DRILL-1335) Merge Join incorrectly return unqualified rows when join key is null.

["Jinfeng Ni (JIRA)" <ji...@apache.org>]

Jinfeng Ni created DRILL-1335:
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             Summary: Merge Join incorrectly return unqualified rows when join key is null. 
                 Key: DRILL-1335
                 URL: https://issues.apache.org/jira/browse/DRILL-1335
             Project: Apache Drill
          Issue Type: Bug
            Reporter: Jinfeng Ni
            Assignee: Jinfeng Ni


Drill's merge join operator incorrectly returns unqualified rows, when join key is null value.  For example,

alter session set `planner.enable_hashjoin` = false;

// Q1
select * from cp.`region.json` t1, cp.`region.json` t2 where t1.non_exist = t2.non_exist2 ;

Q1 should return 0 rows, since both left and right side of join comparison are NULL values. But Drill will return 12100 rows. 

The cause of this problem is MergeJoin operator thinks a comparison between NULL and NULL is a qualified condition, and returns that pair of joining row.





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