Julian Hyde created CALCITE-1489:
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Summary: Add rule, AggegateValuesRule, that applies to Aggregate
on empty relation
Key: CALCITE-1489
URL: https://issues.apache.org/jira/browse/CALCITE-1489
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Assignee: Julian Hyde
Let's call it {{AggregateValuesRule}}, consistent with the naming convention
where we start with the type of rel(s) being acted on. Initially it would apply
to an empty {{Values}}, but potentially it could apply to one or more values.
I don't recall aggregates having a way to tell us what they will return on
empty (or constant) input. In future we could use the constant reducer for
that, but for now, the rule should match a particular set of aggregates:
{{COUNT}} and {{SUM0}} return zero; {{MIN}}, {{MAX}}, {{SUM}} return null. It
must abort if it sees an aggregate it does not know how to handle.
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