If the primary key is missing from the import file, then upon import a sql error was generated when attempting to select the existing data for each line of the import file. This skips processing the individual lines of the file if the primary key is not in the file. No backup primary key is provided/attempted.
If the primary key is missing from the import file, then upon import a sql error was generated when attempting to select the existing data for each line of the import file. This skips processing the individual lines of the file if the primary key is not in the file. No backup primary key is provided/attempted.