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https://issues.apache.org/jira/browse/CALCITE-6817?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17924736#comment-17924736
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ZheHu commented on CALCITE-6817:
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For this case, maybe we can can add a new constructor in RelFieldCollation with
a bool flag (assume calling it shortStringExpanded, which is FALSE by default).
When building a RelNode through RelBuilder, user can set it to TRUE to get
default nulls direction.
However, for those who write SQL to get plan tree, it's still not obvious.
> Add string representation of default nulls direction for RelNode
> ----------------------------------------------------------------
>
> Key: CALCITE-6817
> URL: https://issues.apache.org/jira/browse/CALCITE-6817
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.38.0
> Reporter: ZheHu
> Assignee: ZheHu
> Priority: Minor
> Labels: pull-request-available
>
> Calcite has the same hehavior with Oracle on returning the null direction if
> not specified, which means NULLS LAST is assumed for ASC and NULLS FIRST is
> assumed for DESC.
> However, the default nulls direction is not presented in plan traces. For
> example:
> {code:java}
> select empno from emp order by empno desc
> {code}
> has the following plan:
> {code:java}
> LogicalSort(sort0=[$0], dir0=[DESC])
> LogicalProject(EMPNO=[$0])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
> It makes RelNode clearer if adding nulls direction, so the above plan will be
> like:
> {code:java}
> LogicalSort(sort0=[$0], dir0=[DESC-nulls-first])
> LogicalProject(EMPNO=[$0])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
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