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

[Shang Yuanchun (Jira)]

Benchao Li created FLINK-21573:
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             Summary: 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 / Planner
            Reporter: Benchao Li


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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