[jira] [Created] (FLINK-13392) WindowAggregate inherited from Aggregate incorrectly

["Hequn Cheng (JIRA)" <ji...@apache.org>]

Hequn Cheng created FLINK-13392:
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             Summary: WindowAggregate inherited from Aggregate incorrectly
                 Key: FLINK-13392
                 URL: https://issues.apache.org/jira/browse/FLINK-13392
             Project: Flink
          Issue Type: Improvement
          Components: Table SQL / Planner
            Reporter: Hequn Cheng


As discussed in FLINK-12249, the WindowAggregate inherited from Aggregate incorrectly.

For WindowAggregate, the group keys are window group and normal fields (may be empty), while Aggregate only has normal group keys part, and know nothing about window group key. Currently, many planner rules match and apply transformations on Aggregate, however some of them does not applicable to WindowAggregate, e.g. AggregateJoinTransposeRule, AggregateProjectMergeRule, etc.

Although FLINK-12249 fixes the type equivalence check problem, we should do a step further to correct the WindowAggregate behavior. There are three options now:
 # make Aggregate's group key supports expressions(such as RexCall), not field reference only. and then the window group expression could be as a part of Aggregate's group key. the disadvantage is we must update all existing aggregate rules, metadata handlers, etc.
 # make WindowAggregate extends from SingleRel, not from Aggregate. the disadvantage is we must implement related planner rules about WindowAggregate.
 # in logical phase, we does not merge Aggregate and Project (with window group) into WindowAggregate, and convert the Project to a new kind of node named WindowAssigner, which could prevent Project from being pushed down/merged. and in physical phase, we merge them into WindowAggregate. the advantage is we could reuse current aggregate rules, and the disadvantage is we should add new rules about WindowAssigner.

We could have some further discussions in the jira ticket.



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