Fix unionByName to properly handle missing columns from both DataFrames #243
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When allowMissingColumns=True, the method now correctly handles missing columns from both the left and right DataFrames by: - Adding missing columns from the right DataFrame to the left as NULL - Ensuring all columns from the left DataFrame are present in the right - Properly aligning column order to match Spark's behavior This ensures the union result contains all columns from both DataFrames, with NULL values where columns are missing, matching PySpark behavior.
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Pull request overview
This PR fixes the unionByName method to properly handle missing columns from both DataFrames when allowMissingColumns=True. Previously, the method only handled missing columns from the right DataFrame, but not from the left one.
Key Changes:
- Updated the logic to add NULL columns for missing columns from both DataFrames
- Column order now matches Spark's behavior by prioritizing the left DataFrame's schema
- Added a test case to verify the reversed scenario works correctly
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| duckdb/experimental/spark/sql/dataframe.py | Rewrote the unionByName implementation to handle missing columns bidirectionally and align columns properly before performing the union |
| tests/fast/spark/test_spark_union_by_name.py | Added test case test_union_by_name_allow_missing_cols_rev to verify the fix works when the DataFrame with fewer columns is on the left side |
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Co-authored-by: Copilot <[email protected]>
Co-authored-by: Copilot <[email protected]>
Collaborator
|
Can you fix the linting and formatting errors please? See https://duckdb.org/docs/stable/dev/building/python#3-enable-pre-commit-hooks for guidance. |
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When allowMissingColumns=True, the method now correctly handles missing columns from both the left and right DataFrames by:
This ensures the union result contains all columns from both DataFrames, with NULL values where columns are missing, matching PySpark behavior.