[jira] [Reopened] (FLINK-20059) Outdated SQL docs on aggregate functions' merge

["Jark Wu (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-20059?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jark Wu reopened FLINK-20059:
-----------------------------

> Outdated SQL docs on aggregate functions' merge
> -----------------------------------------------
>
>                 Key: FLINK-20059
>                 URL: https://issues.apache.org/jira/browse/FLINK-20059
>             Project: Flink
>          Issue Type: Bug
>          Components: Documentation, Table SQL / API
>    Affects Versions: 1.12.0, 1.11.2
>            Reporter: Nico Kruber
>            Assignee: Jark Wu
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.12.0
>
>
> In the java docs as well as the user docs, the {{merge}} method of an aggregation UDF is described as optional, e.g.
> {quote}Merges a group of accumulator instances into one accumulator instance. This function must be implemented for data stream session window grouping aggregates and data set grouping aggregates.{quote}
> However, it seems that nowadays this method is required in more cases (I stumbled on this for a HOP window in streaming):
> {code}
> StreamExecGlobalGroupAggregate.scala
>       .needMerge(mergedAccOffset, mergedAccOnHeap, mergedAccExternalTypes)
> StreamExecGroupWindowAggregateBase.scala
>       generator.needMerge(mergedAccOffset = 0, mergedAccOnHeap = false)
> StreamExecIncrementalGroupAggregate.scala
>       .needMerge(mergedAccOffset, mergedAccOnHeap = true, mergedAccExternalTypes)
> StreamExecLocalGroupAggregate.scala
>       .needMerge(mergedAccOffset = 0, mergedAccOnHeap = true)
> {code}



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