I want to assign every record from a particular file the same sequence number in a table, so that I can trace back which records came from which file (i.e. all records from the first file will have value '1', all from the next file will have value '2' etc.)

I will be loading many files to the table. I tried using a sequence with sequencename.currval in my control file, but got message

ORA-08002: sequence SEQUENCENAME.CURRVAL is not yet defined in this session

Is there anyway I can get a value assigned to CURRVAL that will remain the same for each record in the load, or is there some other clever way to do what I want to do ?