[jira] [Commented] (FLINK-7144) Optimize multiple LogicalAggregate into one

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

    [ https://issues.apache.org/jira/browse/FLINK-7144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16394377#comment-16394377 ] 

Rong Rong commented on FLINK-7144:
----------------------------------

Hi [~jark], I am working on FLINK-8688 and I think I can use the fix for this JIRA first before I consolidate all DISTINCT AGG, 

if you haven't started, can I try implementing the optimization for this JIRA together?

> Optimize multiple LogicalAggregate into one
> -------------------------------------------
>
>                 Key: FLINK-7144
>                 URL: https://issues.apache.org/jira/browse/FLINK-7144
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>            Reporter: Jark Wu
>            Priority: Major
>
> When applying multiple GROUP BY, and no aggregates or expression in the first GROUP BY,  and the second GROUP fields is a subset of first GROUP fields. Then the first GROUP BY can be removed. 
> Such as the following SQL , 
> {code}
> SELECT a FROM (SELECT a,b,c FROM MyTable GROUP BY a, b, c) GROUP BY a
> {code}
> should be optimized into 
> {code}
> DataStreamGroupAggregate(groupBy=[a], select=[a])
> DataStreamCalc(select=[a])
> DataStreamScan(table=[[_DataStreamTable_0]])
> {code}
> but get:
> {code}
> DataStreamGroupAggregate(groupBy=[a], select=[a])
> DataStreamCalc(select=[a])
> DataStreamGroupAggregate(groupBy=[a, b, c], select=[a, b, c])
> DataStreamScan(table=[[_DataStreamTable_0]])
> {code}
> I looked for the Calcite built-in rules, but can't find a match one. So maybe we should implement one , and maybe we should implement it in Calcite. 



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