fix: unnest struct field with an alias failed with internal error #19698
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alamb
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alamb
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Jan 8, 2026
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Thanks @kumarUjjawal -- this looks really nice. I have a suggestion for another test too. Let me know what you think
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| ## Basic unnest expression in select struct with alias (alias is ignored for struct unnest) | ||
| query III | ||
| select unnest(struct(1,2,3)) as ignored_alias; |
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Can you also please add a test for the output schema. Perhaps using describe?
Someting like
describe select unnest(struct(1,2,3));
+-------------------------------------------------------------+-----------+-------------+
| column_name | data_type | is_nullable |
+-------------------------------------------------------------+-----------+-------------+
| __unnest_placeholder(struct(Int64(1),Int64(2),Int64(3))).c0 | Int64 | YES |
| __unnest_placeholder(struct(Int64(1),Int64(2),Int64(3))).c1 | Int64 | YES |
| __unnest_placeholder(struct(Int64(1),Int64(2),Int64(3))).c2 | Int64 | YES |
+-------------------------------------------------------------+-----------+-------------+
3 row(s) fetched.
Elapsed 0.007 seconds.
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Yeah, sounds good. Thanks for the feedback.
| query error DataFusion error: Internal error: Assertion failed: struct_allowed: unnest on struct can only be applied at the root level of select expression | ||
| ## Unnest struct with alias - alias is ignored (same as DuckDB behavior) | ||
| ## See: https://github.com/apache/datafusion/issues/12794 | ||
| query TT? |
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Likewise here, it would be great to test the schema output
describe select unnest(column1) c1 from nested_unnest_table;
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Which issue does this PR close?
Rationale for this change
Unnesting with an alias resulted in an internal error it should just be ignored.
What changes are included in this PR?
transformed_root_exprsto only apply to actual struct types (which return multiple expressions)Are these changes tested?
Yes
Are there any user-facing changes?