def _physical_column(self, cube, column_name):
        """ Return the SQLAlchemy Column object matching a given, possibly
        qualified, column name (i.e.: 'table.column'). If no table is named,
        the fact table is assumed. """
        table_name = self.model.fact_table_name
        if '.' in column_name:
            table_name, column_name = column_name.split('.', 1)
        table = cube._load_table(table_name)
        if column_name not in table.columns:
            raise BindingException('Column %r does not exist on table %r' % (
                                   column_name, table_name), table=table_name,
                                   column=column_name)
        return table, table.columns[column_name]