I think you may want to elaborate your insert statement a bit, so that it does not depend on some "hidden" ordering of fields in the database table. If I understood your opening statement, "@map_fields" contains the set of field names to be handled for a given table / set of rows, and "@fields" would store the actual column values for a given row. In that case, something like this would make sense:

  my $fieldnames = join( ",", @map_fields );
  my $parmstring = join( ",", ('?') x scalar @map_fields );
  my $sth = $dbh->prepare( "INSERT INTO $some_tbl ($fieldnames) VALUES
+ ($parmstring)" );

  # loop over rows of data with the execute call:
  ...
      $sth->execute( @fields );
  ...
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This way, as long as your input data provides the correct field labels in the correct order to go with each set of actual data rows, you'll be fine -- having the field names, in a specific order, provided in the insert statement will save you a lot of grief.