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SQL Server Bulk Copy operations (BCP.exe, OpenRowset BULK, …) have specific abilities depending on the data file format specified.
Native (-n) or Format (-f) Files
The data file storage is binary allowing character strings to be stored as single or multi-byte strings on a per column definition. For example columnA can be stored UNICODE and columnB can be stored as single byte or even UTF-8 based string values.
Note: You are not allowed a mix the storage within the same column.
Text files (-c or -w)