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https://issues.apache.org/jira/browse/CALCITE-4616?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17363830#comment-17363830
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Rui Wang commented on CALCITE-4616:
-----------------------------------
The PR seems straightforward: pushing down agg when all inputs have the unique
key. But I am having troubles to understand why unique keys can lead to push
down agg?
> AggregateUnionTransposeRule causes row type mismatch when some inputs have
> unique grouping key
> ----------------------------------------------------------------------------------------------
>
> Key: CALCITE-4616
> URL: https://issues.apache.org/jira/browse/CALCITE-4616
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.26.0
> Reporter: Vladimir Ozerov
> Assignee: Vladimir Ozerov
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.28.0
>
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Consider the following relational tree:
> {code}
> 1: Aggregate[group=a, SUM(b)]
> 2: Union
> 3: Input1[a, b, c]
> 4: Input2[a, b, c]
> {code}
> It may happen, that {{Input1}} has a unique key on {{[a]}}. In this case,
> Apache Calcite, will not install the {{Aggregate}} on top of it, which leads
> to the following tree:
> {code}
> 1: Aggregate[group=a, SUM(b)]
> 2: Union
> 3: Input1[a, b, c]
> 4: Aggregate[group=a, SUM(b)]
> 5: Input2[a, b, c]
> {code}
> Obviously, the tree is incorrect, because {{Union}} inputs now have different
> row types.
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