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https://issues.apache.org/jira/browse/FLINK-21573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17451493#comment-17451493
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Q Kang commented on FLINK-21573:
--------------------------------

Hi [~godfreyhe] [~lzljs3620320] , I've come up with a simple solution to reuse 
scalar function expression in `CodeGeneratorContext`, only when the function is 
deterministic. This solution has been tested in our production environment and 
is good to go. Would you mind assigning this ticket to me? Thx.

> Support expression reuse in codegen
> -----------------------------------
>
>                 Key: FLINK-21573
>                 URL: https://issues.apache.org/jira/browse/FLINK-21573
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table SQL / Runtime
>            Reporter: Benchao Li
>            Priority: Minor
>              Labels: auto-deprioritized-major
>
> Currently there is no expression reuse in codegen, and this may result in 
> more CPU overhead in some cases. E.g.
> {code:java}
> SELECT my_map['key1'] as key1, my_map['key2'] as key2, my_map['key3'] as key3
> FROM (
>   SELECT dump_json_to_map(col1) as my_map
>   FROM T
> )
> {code}
> `dump_json_to_map` will be called 3 times.



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