[jira] [Resolved] (CALCITE-1172) Add rule to flatten two Aggregate operators into one

["Haisheng Yuan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Haisheng Yuan resolved CALCITE-1172.
------------------------------------
       Resolution: Fixed
    Fix Version/s: 1.20.0

Pushed to master, thanks for the review, [~vgarg], [~zhztheplayer]!

> Add rule to flatten two Aggregate operators into one
> ----------------------------------------------------
>
>                 Key: CALCITE-1172
>                 URL: https://issues.apache.org/jira/browse/CALCITE-1172
>             Project: Calcite
>          Issue Type: Bug
>            Reporter: Julian Hyde
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.20.0
>
>          Time Spent: 3h 50m
>  Remaining Estimate: 0h
>
> If there is an Aggregate on top of an Aggregate, and the top aggregate's group key is a subset of the lower aggregate's group key, and the aggregates are expansions of rollups, then a rule would convert into a single aggregate.
> For example, SUM of SUM becomes SUM; SUM of COUNT becomes COUNT; MAX of MAX becomes MAX; MIN of MIN becomes MIN. AVG of AVG would not match, nor would COUNT of COUNT.
> The rule would convert
> {noformat}
> Aggregate({x}, SUM(c1), MIN(c2), MAX(c3))
>   Aggregate({x, y}, SUM(c1), MIN(c2), MAX(c3))
>     R
> {noformat}
> into
> {noformat}
> Aggregate({x}, SUM(c1), MIN(c2), MAX(c3))
>   R
> {noformat}
> The rule would not work if there was anything between the two {{Aggregate}} operators.
> The implementation would use {{SqlSplittableAggFunction}} to deduce rollups, and in fact would be practically the converse of {{AggregateExchangeTransposeRule}} proposed in CALCITE-907.



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