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https://issues.apache.org/jira/browse/CALCITE-4350?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17219843#comment-17219843
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Julian Hyde commented on CALCITE-4350:
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Yes, good catch. I intended to make {{reverse()}} non-lossy when I refactored
it in
[1ba5c35|https://github.com/apache/calcite/commit/1ba5c3559eb116af11c10d45907faefb5755f546]
but I forgot. All calls to {{reverse()}} are currently followed by a call to
{{lax()}} so this is a safe change to make. Let's make it soon.
> The reverse operation of collation direction is overly relaxed
> --------------------------------------------------------------
>
> Key: CALCITE-4350
> URL: https://issues.apache.org/jira/browse/CALCITE-4350
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
>
> For the current implementation, {{RelFieldCollation#Direction#reverse}}
> returns \{{DESCENDING}} for \{{STRICTLY_ASCENDING}}, and returns
> \{{ASCENDING}} for {{STRICTLY_DESCENDING}}.
> This is overly relaxed. In a strict manner, it should return
> \{{STRICTLY_DESCENDING}} for \{{STRICTLY_ASCENDING}}, and vice versa.
> If the user needs to get the relaxed reverse direction, they may call
> \{{collation.getDirection().reverse().lax();}}, as in many places of our code
> base.
> Do you agree?
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