[jira] [Updated] (IGNITE-20009) Sql. Rework 2-phase aggregates part 2. AVG as SUM / COUNT.

["Konstantin Orlov (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/IGNITE-20009?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Konstantin Orlov updated IGNITE-20009:
--------------------------------------
    Fix Version/s: 3.0.0-beta2

> Sql. Rework 2-phase aggregates part 2. AVG as SUM / COUNT.
> ----------------------------------------------------------
>
>                 Key: IGNITE-20009
>                 URL: https://issues.apache.org/jira/browse/IGNITE-20009
>             Project: Ignite
>          Issue Type: Improvement
>          Components: sql
>    Affects Versions: 3.0.0-beta1
>            Reporter: Maksim Zhuravkov
>            Assignee: Maksim Zhuravkov
>            Priority: Minor
>              Labels: ignite-3
>             Fix For: 3.0.0-beta2
>
>          Time Spent: 4h 20m
>  Remaining Estimate: 0h
>
> Map/reduce implementation of some aggregates requires replacing an aggregate with a combination of aggregates. For example AVG(col) should be implemented as 
> MAP: SUM(col)  sum_col, COUNT (col) as count_col
> REDUCE: SUM(sum_col)/SUM(COUNT(count_col))
> To implement AVG for two phase aggregation we need the following changes:
> - Replace AVG on MAP phase with SUM and COUNT. 
> - Change rowType produced by MAP phase/accepted by REDUCE phase.
> - Add a projection after a reduce aggregate that includes division and produces final result (it obviously should include other results of other aggregates in the correct order). Divisor should be checked for 0 in order not to trigger division by zero error.
> Calcite has `AggregateReduceFunctionsRule` that rewrites AVG aggregate (see reduceAvg method) that code can be used a reference.



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