Review Request 37339: DRILL-3574: Empty Over Clause should trigger Union-Exchange to be added below

[Sean Hsuan-Yi Chu]

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https://reviews.apache.org/r/37339/
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Review request for drill and Aman Sinha.


Bugs: DRILL-3574
    https://issues.apache.org/jira/browse/DRILL-3574


Repository: drill-git


Description
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For the empty Over-Clause, make DrillDistributionTrait to be as SINGLETON


Diffs
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exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/DrillDistributionTrait.java
 c1e241d 
  
exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/WindowPrule.java
 034fd47 
  exec/java-exec/src/test/java/org/apache/drill/exec/TestWindowFunctions.java 
ce5a477 

Diff: https://reviews.apache.org/r/37339/diff/


Testing
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All required


Thanks,

Sean Hsuan-Yi Chu