def _create_table(self):
        '''
        create the current table if not exists
        '''
        self._cursor.execute('''
            CREATE TABLE IF NOT EXISTS %(name)s ( %(fields)s )
        ''' % {
            'name': self._name,
            'fields': ','.join('%s %s' % (k, v) for (k, v) in self._fields)
        })
        self._connection.commit()
create the current table if not exists