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https://issues.apache.org/jira/browse/CALCITE-7104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18010147#comment-18010147
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Zhen Chen commented on CALCITE-7104:
------------------------------------

[~julianhyde] I tried writing a simple implementation. Could you please check 
if it aligns with your ideas? The PR link is 
https://github.com/apache/calcite/pull/4480  .

> Remove duplicate sort keys
> --------------------------
>
>                 Key: CALCITE-7104
>                 URL: https://issues.apache.org/jira/browse/CALCITE-7104
>             Project: Calcite
>          Issue Type: Improvement
>            Reporter: weihua zhang
>            Priority: Major
>              Labels: pull-request-available
>
> {code:sql}
> select d1 from  (select deptno as d1, deptno as d2 from dept ) as tmp order 
> by d1, d2;
> {code}
> {noformat}
> LogicalProject(D1=[$0]), id = 2284
>   LogicalSort(sort0=[$0], sort1=[$1], dir0=[ASC], dir1=[ASC]), id = 2283
>     LogicalProject(D1=[$0], D2=[$0]), id = 2282
>       LogicalTableScan(table=[[default, dept]]), id = 2278
> {noformat}
> LogicalSort can change to:
> {noformat}
> LogicalProject(D1=[$0]), id = 2284
>   LogicalSort(sort0=[$0], dir0=[ASC]), id = 2283
>     LogicalProject(D1=[$0], D2=[$0]), id = 2282
>       LogicalTableScan(table=[[default, dept]]), id = 2278
> {noformat}



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