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https://issues.apache.org/jira/browse/CALCITE-5894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17753803#comment-17753803
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Julian Hyde commented on CALCITE-5894:
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I just read the “Fundamental Techniques” paper. I see that the authors rely on
functional dependencies, as we have been discussing.
However, one section of the paper discusses “order homogenization”, including
recognizing columns that will satisfy an interesting order *based on filters
that have not yet been applied*. Those scenarios seem important, and are not
covered by work we have been discussing. Do you think we should log a follow-up
case for that work?
> Add SortRemoveRedundantRule to remove redundant sort fields if they are
> functionally dependent on other sort fields
> -------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-5894
> URL: https://issues.apache.org/jira/browse/CALCITE-5894
> Project: Calcite
> Issue Type: New Feature
> Reporter: JingDas
> Assignee: JingDas
> Priority: Minor
> Labels: pull-request-available
>
> In some scene, Sort fields can be reduct, if sort fields contain unique key
> For example
> {code:java}
> SELECT ename, salary FROM Emp
> order by empno, ename{code}
> where `empno` is a key, `ename` is redundant since `empno` alone is
> sufficient to determine the order of any two records.
> So the SQL can be optimized as following:
> {code:java}
> SELECT name, Emp.salary FROM Emp
> order by empno{code}
> For another example:
> {code:java}
> SELECT e_agg.c, e_agg.ename
> FROM
> (SELECT count(*) as c, ename, job FROM Emp GROUP BY ename, job) AS e_agg
> ORDER BY e_agg.ename, e_agg.job, e_agg.c {code}
> Although `e_agg.ename` is not a key but field `ename` is unique and not null,
> it can be optimized as following:
> {code:java}
> SELECT e_agg.c, e_agg.ename
> FROM (SELECT count(*) as c, ename, job FROM Emp GROUP BY ename, job) AS e_agg
> ORDER BY e_agg.ename, e_agg.job{code}
> Sorting is an expensive operation, however. Therefore, it is imperative that
> sorting
> is optimized to avoid unnecessary sort field.
>
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