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https://issues.apache.org/jira/browse/CALCITE-4615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17349435#comment-17349435
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Julian Hyde commented on CALCITE-4615:
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It's worth considering cases such as where the inputs are SMALLINT and BIGINT.
Casting will be required.
This is UNION ALL, right? The rule won't fire on UNION DISTINCT.
Aggregate with empty grouping key is a special case. It is the only case where
SUM applied to a NOT NULL column can return a NULL result. (Because if the
input is empty it will aggregate a group of 0 rows.) It's worth exploring cases
with a non-empty grouping key also.
> AggregateUnionTransposeRule may assign wrong aggregate function to input
> ------------------------------------------------------------------------
>
> Key: CALCITE-4615
> URL: https://issues.apache.org/jira/browse/CALCITE-4615
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.26.0
> Reporter: Vladimir Ozerov
> Priority: Major
>
> Consider the following query tree:
> {code}
> 1: Aggregate[SUM($0):BIGINT]
> 2: Union[$0:BIGINT]
> 3: Input[$0:BIGINT]
> 4: Input[$0:BIGINT NOT NULL]
> {code}
> The Union's row type is {{BIGINT}}, and Aggergate's row type is {{BIGINT}} as
> well.
> When the {{AggregateUnionTransposeRule}} rule pushes {{Aggregate}} below
> {{Union}}, it installs the aggregate call from the original {{Aggregate}} to
> new aggregates:
> {code}
> 1: Aggregate[SUM($0):BIGINT]
> 2: Union[$0:BIGINT]
> 3: Aggregate[SUM($0):BIGINT]
> 4: Input[$0:BIGINT]
> 5: Aggregate[SUM($0):BIGINT]
> 6: Input[$0:BIGINT NOT NULL]
> {code}
> This leads to a Litmus failure in the {{Aggregate}} on line 5 because the
> aggregate call returns {{BIGINT}}, while it should return {{BIGINT NOT NULL}}.
> The solution is to re-create aggregate calls for inputs and let Calcite
> deduce the return type.
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