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feat: add match_columns_by_header option for CSV - #27021
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November 2, 2026 21:16
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Thanks @wyatt-herkamp —the per-file schema plus BatchAdapter design is a good fit for DataFusion! Header discovery currently fails on leading blank records and BOM-prefixed comments, and the primary CsvReadOptions Rust API cannot enable the feature. How about aligning header discovery with Arrow’s CSV parsing semantics, adding regressions for those cases, exposing the option through CsvReadOptions, and marking/documenting the breaking API addition? |
…y_header on CsvReadOptions Header discovery now skips a leading UTF-8 BOM, blank records and comment lines the same way csv-core does, so files with those before the header are mapped by name rather than silently read by position.
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Thanks for the review @xudong963. Addressed in 70ec58c and rebased on main:
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Which issue does this PR close?
Rationale for this change
arrow-csv parses columns by position, so when reading multiple CSV files where some file is missing a column (that isn't the last one), values land in the wrong columns or parsing fails.
What changes are included in this PR?
match_columns_by_headerCSV option (config,CsvFormat,CsvSource, and proto).has_header), each file's header is read and its columns are mapped to the table schema by name; missing columns are filled viaPhysicalExprAdapterFactory. Works for both full-file and range (repartitioned) reads.CsvReadOptions::match_columns_by_headerexposes the option on theread_csvAPI.Are these changes tested?
Yes: unit tests in
datasource-csv/src/source.rsandcore/src/datasource/physical_plan/csv.rs, a proto round-trip test, and sqllogictest cases incsv_files.slt.Are there any user-facing changes?
New opt-in
format.match_columns_by_headeroption, documented informat_options.md. Default behavior is unchanged.API change:
CsvOptionsandCsvReadOptionsgain a publicmatch_columns_by_headerfield, and the protobufCsvOptions/CsvScanExecNodemessages gain the same field. Exhaustive struct literals need updating; noted in the 56.0.0 upgrade guide.