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https://issues.apache.org/jira/browse/CALCITE-600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14326656#comment-14326656
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Jesus Camacho Rodriguez commented on CALCITE-600:
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The default factory creates {{LogicalUnion}} operators indeed; but now we can
provide a factory that creates our own kind of operators that extend the base
{{Union}} class. The matching will be based on the {{Union}} base class.
A given use case can be found in Hive. There is a {{HiveUnion}} operator that
extends {{Union}}. I would like to use the UnionMerge rule in Hive. Without
this extension, the only solution is to extend the rule and rewrite the
{{match}} (and possibly {{transform}}) methods. Instead, now we will match on
base class and providing the UnionFactory to create {{HiveUnion}} operators, as
other rules already do.
> Create UnionFactory and use in rules containing Union operator
> --------------------------------------------------------------
>
> Key: CALCITE-600
> URL: https://issues.apache.org/jira/browse/CALCITE-600
> Project: Calcite
> Issue Type: Bug
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
>
> Union related rules match on {{LogicalUnion}} and use this implementation to
> create the new Union operators. As it is done for other rules, a Union
> factory can be created and used by them, so subclasses that extend Union can
> use the rules.
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