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https://issues.apache.org/jira/browse/FLINK-3498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15174074#comment-15174074
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ASF GitHub Bot commented on FLINK-3498:
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Github user twalthr commented on the pull request:
https://github.com/apache/flink/pull/1747#issuecomment-190825143
"quite a bit of code at various places": Yes, you are right. I already
tried to simplify it as much as I can. The problem is that we have 3 APIs that
all have slightly different requirements. I chose `TRIM` because it is an
extreme example. Other functions (80%) are easier, because they don't need
their own code generator and ExpressionParser.
My current implementation has a proper separation of the different layers:
Expression API -> RexNodeTranslator -> CodeGen
3 layers + 3 APIs = up to 6 files to change for every function.
I don't know if it makes sense to mix the layers.
> Implement TRIM, SUBSTRING as reference design for Table API
> -----------------------------------------------------------
>
> Key: FLINK-3498
> URL: https://issues.apache.org/jira/browse/FLINK-3498
> Project: Flink
> Issue Type: Sub-task
> Components: Table API
> Reporter: Timo Walther
> Assignee: Timo Walther
>
> As described in FLINK-3497 TRIM and SUBSTRING are the first scalar functions
> implemented in Calcite and used in Table API.
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