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