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https://issues.apache.org/jira/browse/CALCITE-7104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18009812#comment-18009812
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Zhen Chen commented on CALCITE-7104:
------------------------------------
Thank you very much for [~julianhyde]'s detailed reply. I completely agree with
this implementation approach. I was previously trying to see if an Md* could be
used as a utility class to perform equality checks for expressions, but it now
seems that functional dependency is indeed a more general method. I think the
current JIRA can be temporarily suspended. Once functional dependency is
implemented, it will better handle the elimination of duplicate sort keys (and
may also include a general rule covering SORT, AGG, and some RelNodes with
column pruning effects). I might need to spend some time first thoroughly
understanding all the discussions in the JIRAs you provided to see if I can
attempt to implement CALCITE-5913 first.
> 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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