@classmethod
def sql_fields(cls):
    """
        Returns a list of all SQL fields across all tables for this
        entity, including derived fields. This method can be used
        in conjunction with `nfldb.Entity.from_row_tuple` to quickly
        create new `nfldb` objects without every constructing a dict.
        """
    if not hasattr(cls, '_cached_sql_fields'):
        cls._cached_sql_fields = cls._sql_columns()
        cls._cached_sql_fields += cls._sql_tables['derived']
    return cls._cached_sql_fields
