[jira] [Created] (CALCITE-2216) Improve extensibility of AggregateReduceFunctionsRule

["Fabian Hueske (JIRA)" <ji...@apache.org>]

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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