Fabian Hueske created CALCITE-2216:
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Summary: Improve extensibility of AggregateReduceFunctionsRule
Key: CALCITE-2216
URL: https://issues.apache.org/jira/browse/CALCITE-2216
Project: Calcite
Issue Type: Improvement
Components: core
Affects Versions: 1.15.0
Reporter: Fabian Hueske
Assignee: Julian Hyde
I'm proposing to improve the extensibility of {{AggregateReduceFunctionsRule}}.
The purpose of the rule is to decompose complex aggregation functions like
{{VAR_POP}} and {{STDDEV_SAMP}} into {{COUNT}} and {{SUM}} functions and
compute the original functions in a subsequent Calc operator.
Right now, the rule class provides a {{protected}} method that can be
overridden to create an {{Aggregate}} with the updated aggregate calls.
We are using the rule in Flink and have a special {{Aggregate}} Rel for
group-windowed aggregations ({{GROUP BY TUMBLE/HOP/SESSION}}). Our
implementation requires to forward some additional fields from the
{{Aggregate}} for window properties like {{TUMBLE_START}} or {{HOP_END}}. In
the current form, we cannot extend the rule, because these fields are striped
off by the {{Calc}} node that is automatically added by the rule.
I'm proposing to also move the code to create the {{Calc}} into a {{protected}}
method just like the code to create the new {{Aggregate}}.
I know, this is a fairly Flink-specific issue, but the code changes are minimal
(no change in functionality) and it would help us, because we would not need to
copy the rule and maintain it in Flink.
I'll open a PR for this. Looking forward to your comments.
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