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https://issues.apache.org/jira/browse/FLINK-5956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15895382#comment-15895382
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ASF GitHub Bot commented on FLINK-5956:
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Github user shaoxuan-wang commented on the issue:

    https://github.com/apache/flink/pull/3470
  
    @fhueske, we should add different built-in aggregates for the ones that are 
not easy to be retracted (for instance Max and Min), one as withRetract(used 
for over window as # of items are limited, also for the dataStream when 
retraction is absolute needed) the other one as withoutRetract (used for 
dataSet and dataStream where retraction is not needed), it is the optimizer to 
check the rules and decide which aggregate should be used. I think we can go 
ahead as this (withRetract) for now, and complete the entire design together 
with dataStream retraction.


> Add retract method into the aggregateFunction
> ---------------------------------------------
>
>                 Key: FLINK-5956
>                 URL: https://issues.apache.org/jira/browse/FLINK-5956
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Table API & SQL
>            Reporter: Shaoxuan Wang
>            Assignee: Shaoxuan Wang
>
> Retraction method is help for processing updated message. It will also very 
> helpful for window Aggregation. This PR will first add retraction methods 
> into the aggregateFunctions, such that on-going over window Aggregation can 
> get benefit from it.



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