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Description
Feature Request / Improvement
This issue tracks implementation for all column projections.
From the spec,
Columns in Iceberg data files are selected by field id. The table schema's column names and order may change after a data file is written, and projection must be done using field ids.
Values for field ids which are not present in a data file must be resolved according the following rules:
- Return the value from partition metadata if an Identity Transform exists for the field and the partition value is present in the partition struct on data_file object in the manifest. This allows for metadata only migrations of Hive tables. (Resolved by API table.scan does not conform to Iceberg spec for identity partition columns #1401)
- Use schema.name-mapping.default metadata to map field id to columns without field id as described below and use the column if it is present.
- Return the default value if it has a defined initial-default (See Default values section for more details). (Support reading initial-defaults #1644)
- Return null in all other cases.
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