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Posted to github@datafusion.apache.org by "LiaCastaneda (via GitHub)" <gi...@apache.org> on 2026/09/07 10:53:01 UTC

[I] Nested struct field access on lambda parameters is unsupported (SQL and Substrait) [datafusion]

LiaCastaneda opened a new issue, #25017:
URL: https://github.com/apache/datafusion/issues/25017

   ### Is your feature request related to a problem or challenge?
   
   `e.field` doesn't resolve when `e` is a lambda parameter of struct type, in both the SQL frontend and the Substrait consumer path. Accessing the same nested field on an ordinary struct-typed column works fine in both -- this is specific to lambda-bound variables.
   
   ### To Reproduce
   
   ```
   -- Works: whole lambda parameter, no dotted access. Real field names
   -- (rule_number, rule_action) survive into the output type.
   SELECT array_transform(
     make_array(named_struct('rule_number', 1, 'rule_action', 'allow')),
     e -> e
   );
   
   -- Fails: dotted access into the lambda parameter's own struct fields.
   SELECT array_transform(
     make_array(named_struct('rule_number', 1, 'rule_action', 'allow')),
     e -> e.rule_action
   );
   ```
   
   The second query fails with `Schema error: No field named e.rule_action`. -- even purely in the SQL planner, no Substrait involved.
   
   
   
   ### Describe the solution you'd like
   
   Support referencing a field in the struct type inside a lambda (in both paths)
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   _No response_


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Re: [I] Nested struct field access on lambda parameters is unsupported (SQL and Substrait) [datafusion]

Posted by "LiaCastaneda (via GitHub)" <gi...@apache.org>.
LiaCastaneda commented on issue #25017:
URL: https://github.com/apache/datafusion/issues/25017#issuecomment-5600515195

   ok not sure this is super urgent actually, we can use `get_field` and it will work
   ```
   SELECT array_transform(
     make_array(named_struct('rule_number', 1, 'rule_action', 'allow')),
     e -> get_field(e, 'rule_action')
   );
   ```
   


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Re: [I] Nested struct field access on lambda parameters is unsupported (SQL and Substrait) [datafusion]

Posted by "LiaCastaneda (via GitHub)" <gi...@apache.org>.
LiaCastaneda commented on issue #25017:
URL: https://github.com/apache/datafusion/issues/25017#issuecomment-5601459873

   the roundtrip (SQL -> substrait -> SQL) for this one will not work though 
   ```
   SET datafusion.sql_parser.dialect = 'DuckDB';   -- needed just to parse `x -> expr` lambda syntax at all
   
   WITH test_data AS (
       SELECT named_struct(
           'label', 'example',
           'items', [
               named_struct('name', 'first', 'value', 2),
               named_struct('name', 'second', 'value', 5)
           ]
       ) AS row_col
   )
   SELECT
       row_col.label,
       array_transform(row_col.items, item -> get_field(item, 'value') * 10) AS scaled_values
   FROM test_data;
   ```


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