[jira] [Commented] (FLINK-21573) Support expression reuse in codegen

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

    [ https://issues.apache.org/jira/browse/FLINK-21573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17376399#comment-17376399 ] 

Shuo Cheng commented on FLINK-21573:
------------------------------------

This is related to this Calcite JRIA [CALCITE-3760|https://issues.apache.org/jira/browse/CALCITE-3760]

i.e., projects contains non-deterministic operators cannot merged.

> 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: Major
>              Labels: stale-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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