liningpan opened a new issue, #23655:
URL: https://github.com/apache/datafusion/issues/23655
### Is your feature request related to a problem or challenge?
Since UDF can only return a single column as output, returning a
`StructArray` is desired in many cases. However, accessing fields of the
returned struct results in redundant calls to the UDF.
```sql
SELECT
example_struct(c)['a'],
example_struct(c)['b']
FROM (SELECT unnest(range(1,100)) as c)
```
Datafusion produces the following projection step for the query, resulting
in calling the UDF with the same column twice.
```
ProjectionExec: expr=[get_field(example_struct(c@0), a) as
example_struct(c)[a], get_field(example_struct(c@0), b) as example_struct(c)[b]]
```
Note that calling the UDF in a CTE or view does not change the execution
plan.
Here is a minimal example
[https://github.com/liningpan/udf-get-field-optimization].
### Describe the solution you'd like
@adriangb mentioned that CSE (Common Sub-expression Elimination) optimizer
might be able to handle this.
### Describe alternatives you've considered
_No response_
### Additional context
_No response_
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