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https://issues.apache.org/jira/browse/CALCITE-4160?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17188696#comment-17188696
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Julian Hyde commented on CALCITE-4160:
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Interesting research, [~zabetak]. But the issue remains: if we allow ORDER BY
in sub-queries, when is it safe/valid to remove the Sort without affecting
semantics. As I have noted, if people use a view that contains ORDER BY in a
query, the algebra for that query will now contain a Sort but the Sort is
probably not necessary for correctness, and implementing it will make the plan
less efficient.
> 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
> Labels: pull-request-available
> Attachments: image-2020-08-07-10-48-59-599.png,
> image-2020-08-07-10-50-22-351.png
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> 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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