@classmethod
def __update_table(cls, table: str=None, where: dict=None, **kwargs):
    """        Build update statement.

        :param table:
            target table name from the data base
        :param where:
            kargs for a MySQL WHERE clause of key=value

        :return
            MySQL update statement
        """
    t = []
    for k, v in kwargs.items():
        if v != 'NULL' and isinstance(v, str):
            t.extend([k, f"'{v}'"])
        else:
            t.extend([k, str(v)])
    cols = ','.join(['%s=%s'] * len(kwargs)) % tuple(t)
    key, val = [[k, v] for k, v in where.items()][0]
    que = f"UPDATE {table} SET {cols} WHERE {key}='{val}'"
    return que
