[jira] [Commented] (FLINK-27145) The code generated for agg function accepts empty parameters can't be compiled

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

    [ https://issues.apache.org/jira/browse/FLINK-27145?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17519550#comment-17519550 ] 

luoyuxia commented on FLINK-27145:
----------------------------------

[~lzljs3620320] Could you please have a look? If it's a problem that should be fixed, I would like to take it.

> The code generated for agg function accepts empty parameters can't be compiled
> ------------------------------------------------------------------------------
>
>                 Key: FLINK-27145
>                 URL: https://issues.apache.org/jira/browse/FLINK-27145
>             Project: Flink
>          Issue Type: Bug
>          Components: Table SQL / Planner
>            Reporter: luoyuxia
>            Priority: Major
>             Fix For: 1.16.0
>
>
> In batch mode, when I try to call Hive's `count` function(GenericUDAFCount) using the following sql:
> {code:java}
> select count(*) from src;
> {code}
> It'll throw the exception "Unexpected token ")" in primary" while compling the generated code.
> It happens in the following generated code:
> {code:java}
> function_org$apache$flink$table$planner$utils$xxx.accumulate(
>             acc$7,); {code}
>  
> The reason is the following code in  method `AggCodeGenHelper#genAccumulateFlatAggregateBuffer`
> {code:java}
> s"""
>   |$externalAccTypeTerm $externalAccTerm = $externalAccCode;
>   |${functionIdentifiers(function)}.accumulate(
>   |  $externalAccTerm,
>   |  ${operandTerms.mkString(", ")}); // but operandTerms can be empty list
>   |$aggBufferName = ${genToInternalConverter(ctx, externalAccType)(externalAccTerm)};
>   |${aggBufferExpr.nullTerm} = false;
> """.stripMargin {code}
> In this case, for count(\*), it'll be regarded as an agg function with empty parameter in Hive.
> So, the exception happens.
> Although the agg function with empty parameter is rare, it may happens. We should make the code more rubst.



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