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https://issues.apache.org/jira/browse/DRILL-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14567769#comment-14567769
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Sean Hsuan-Yi Chu commented on DRILL-3130:
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Review completed at :
https://reviews.apache.org/r/34528/
Commit#: bca20655283d351d5f5c4090e9047419ff22c75e
> 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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