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https://issues.apache.org/jira/browse/CALCITE-5705?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stamatis Zampetakis resolved CALCITE-5705.
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Resolution: Fixed
Fixed in
https://github.com/apache/calcite/commit/f32289870be80e69dabc5b7e24bd6c777d4eb688.
> Generalize RemoveEmptySingleRule to work with arbitrary relations and pruning
> configurations
> --------------------------------------------------------------------------------------------
>
> Key: CALCITE-5705
> URL: https://issues.apache.org/jira/browse/CALCITE-5705
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Stamatis Zampetakis
> Assignee: Stamatis Zampetakis
> Priority: Major
> Fix For: 1.35.0
>
>
> Currently
> [RemoveEmptySingleRule|https://github.com/apache/calcite/blob/b0b27e8872b33c5ab203e0e2365d267a594c80be/core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java#LL285C23-L285C44]
> can only transform {{SingleRel}} relations to empty. However, the logic
> inside the {{matches}} method is at the most part capable of handling any
> kind of relation including those that have multiple children.
> By generalizing the {{RemoveEmptySingleRule}} to work with arbitrary
> relations we can refactor other pruning rules such as those created by
> [CorrelateLeftEmptyRuleConfig|https://github.com/apache/calcite/blob/b0b27e8872b33c5ab203e0e2365d267a594c80be/core/src/main/java/org/apache/calcite/rel/rules/PruneEmptyRules.java#L588]
> without the need for creating more classes and duplicating code.
> Moreover by changing the constructor to accept {{PruneEmptyRule.Config}}
> instead of {{RemoveEmptySingleRuleConfig}} we can reduce code duplication
> further since configurations such as {{ZeroMaxRowsRuleConfig}} and
> {{SortFetchZeroRuleConfig}} could be modified to create instances of
> {{RemoveEmptySingleRule}}.
> This is mainly a refactoring to simplify pruning rules and remove duplicate
> logic. The change is fully backwards compatible.
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