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https://issues.apache.org/jira/browse/CALCITE-5894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17751021#comment-17751021
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LakeShen commented on CALCITE-5894:
-----------------------------------

I think this rule maybe a RBO rule(TransformationRule),when this rule is 
matched,It is not aware of the distribution information of the underlying data.

When we generate a distributed plan, we don't need to perform additional sorts 
if the underlying data satisfies the ordering requirements of the upper layer.

I think they're two orthogonal points.So in my point, I think it makes sense to 
have this rule.The user of calcite decides whether use this rule.

> Add SortRemoveRedundantRule to remove redundant sort fields if sort fields 
> contains unique key
> ----------------------------------------------------------------------------------------------
>
>                 Key: CALCITE-5894
>                 URL: https://issues.apache.org/jira/browse/CALCITE-5894
>             Project: Calcite
>          Issue Type: New Feature
>            Reporter: JingDas
>            Assignee: JingDas
>            Priority: Minor
>
> 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.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{code}
> Sorting is an expensive operation, however. Therefore, it is imperative that 
> sorting
> is optimized to avoid unnecessary sort field.
>  



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