adriangb commented on issue #12010:
URL: https://github.com/apache/datafusion/issues/12010#issuecomment-2291247886

   To give a concrete examples, we might have a schema evolution that looks 
like:
   ```
   day=2020-01-01/1.parquet  - (name Utf8, department Utf8)
   -- department column made a partition
   day=2020-01-02/department=abc/1.parquet  - (name Utf8,)
   -- added salary column
   day=2020-01-03/department=abc/1.parquet  - (name Utf8, salary Float32)
   -- department moved back to a regular column
   day=2020-01-04/1.parquet  - (name Utf8, salary Float32, department Utf8)
   -- name made LargeUtf8 (or Utf8View, etc.)
   day=2020-01-05/1.parquet  - (name LargeUtf8, salary Float32, department Utf8)
   ```
   Where our "final"/"current" table schema is `(day Date32, name LargeUtf8, 
salary Float32, department Utf8)`.
   
   (fwiw in reality some of these columns, e.g. `department`, would be 
dict-encoded)


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