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https://issues.apache.org/jira/browse/CALCITE-6852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17929698#comment-17929698
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Zhen Chen commented on CALCITE-6852:
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[~asolimando] I mean, we can not discuss the issue of ProjectRemoveRule first,
but current discuss the issue that findBestExpr will select the wrong Project
when Project has different aliases. I think aliases are very important in SQL,
especially in the Project operator. If this issue is not fixed,
ProjectAggregateMergeRule will also have the problem of alias loss. If you
think this problem does not need to be modified, should you mark the relevant
rules as "alias loss may occur, please pay attention to the order of multiple
rules", otherwise this issue will continue to be raised. Aliases are a very
important point in other databases.
> Project's digest calculation error, should include FieldNames in rowType
> -------------------------------------------------------------------------
>
> Key: CALCITE-6852
> URL: https://issues.apache.org/jira/browse/CALCITE-6852
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.39.0
> Reporter: Zhen Chen
> Assignee: Zhen Chen
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.39.0
>
> Attachments: image-2025-02-22-17-19-46-706.png,
> image-2025-02-23-16-47-22-367.png, image-2025-02-23-16-53-03-724.png
>
>
> When I was building test cases for CALCITE-6850, I found that the results did
> not meet my expectations. When debugging the code, I discovered that the
> project's digest calculation did not include column names, This leads to the
> inability to correctly find the correct project during the findBestExp
> process.
> debug picture:
> !image-2025-02-22-17-19-46-706.png|width=553,height=245!
> I think we need to add column names in computing project's degist like this:
> {code:java}
> // code now
> protected int deepHashCode0() {
> return Objects.hash(traitSet, input.deepHashCode(), exps, hints);
> }
> // should change to
> protected int deepHashCode0() {
> return Objects.hash(traitSet, input.deepHashCode(),
> exps, hints, getRowType().getFieldNames());
> }{code}
> This change will affect some cases and the results of these cases need to be
> fixed.
>
> If calcite need this change, I can pull a pr. If this issue is not fixed,
> there will be no way to find a case for issue CALCITE-6850.
>
> supplement：
> !image-2025-02-23-16-47-22-367.png|width=518,height=274!
> !image-2025-02-23-16-53-03-724.png|width=521,height=284!
> If project fields is not nested, then it wil use field name as pw key, and
> expr as pw value,but in deepHashCode(), only use pw value to compute hash
> code. So other operators has no effect. Such as Agg, it use the aggCalls as
> pw value.
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