[jira] [Created] (DRILL-3130) Project can be pushed below union all / union to improve performance

["Sean Hsuan-Yi Chu (JIRA)" <ji...@apache.org>]

Sean Hsuan-Yi Chu created DRILL-3130:
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             Summary: Project can be pushed below union all / union to improve performance
                 Key: DRILL-3130
                 URL: https://issues.apache.org/jira/browse/DRILL-3130
             Project: Apache Drill
          Issue Type: Improvement
          Components: Query Planning & Optimization
            Reporter: Sean Hsuan-Yi Chu
            Assignee: Sean Hsuan-Yi Chu


A query such as 
{code}
Select a from 
(select a, b, c, ..., union all select a, b, c, ...)
{code}
will perform Union-All over all the specified columns on the two sides, despite the fact that only one column is asked for at the end. Ideally, we should perform ProjectPushDown rule for Union & Union-All to avoid them to generate results which will be discarded at the end.



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