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https://issues.apache.org/jira/browse/CALCITE-4160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17172995#comment-17172995
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Julian Hyde commented on CALCITE-4160:
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[~danny0405], That may be the case. However they may have defined a view with
an ORDER BY clause (for presentation purposes) and have used that view in a
join query. In that case they may not be pleased paying a performance penalty
because Calcite does not use a perfectly valid optimization.
Hints may be a good solution to this problem. Users could add a hint to their
SQL if they want the ORDER BY retained. Otherwise Calcite will remove it, per
the standard.
> Add configuration to retain ORDER BY in sub-query
> -------------------------------------------------
>
> Key: CALCITE-4160
> URL: https://issues.apache.org/jira/browse/CALCITE-4160
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Jiatao Tao
> Assignee: Jiatao Tao
> Priority: Minor
> Attachments: image-2020-08-07-10-48-59-599.png,
> image-2020-08-07-10-50-22-351.png
>
>
> Pre discussion see in
> https://issues.apache.org/jira/browse/CALCITE-2798
> https://issues.apache.org/jira/browse/CALCITE-3664
> IMO, we should at least provide a configuration about this. People use
> Calcite most for its optimizer, and this info users may care, How it executed
> is by the engine, but users should know this in the plan.
>
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