Kontinuation opened a new pull request, #17524:
URL: https://github.com/apache/datafusion/pull/17524

   ## Which issue does this PR close?
   
   - Closes #17422.
   
   ## Rationale for this change
   
   As reported by #17422, extension metadata was dropped in some queries 
involving subqueries. This happens when a column references another column in a 
correlated subquery, which creates an `OuterReferenceColumn` in DataFusion's 
logical plan.
   
   `OuterReferenceColumn` is defined to contain a data type and a referenced 
column. As we know, outer reference column refers to a field in another table, 
so there's no way to retrieve the field metadata of referenced column given the 
schema of the current table. To overcome this problem, we define 
`OuterReferenceColumn` to contain the entire referenced field as a `FieldRef`. 
We also updated the implementation of `to_field` to return the referenced 
field, which contains the original metadata of referenced field.
   
   ## What changes are included in this PR?
   
   Changed `OuterReferenceColumn` to contain the referenced outer field as a 
`FieldRef`.
   
   ## Are these changes tested?
   
   * Added a unit test
   * Added the repro in the issue to `user_defined_scalar_functions` test
   
   ## Are there any user-facing changes?
   
   Yes. This changes part of the public API.
   


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