Refs #2443 -- fixed format_dtdelta on SQLite

        - A string representing a datetime

    """

    try:

        if isinstance(lhs, int):

        if isinstance(lhs, six.integer_types):

            lhs = str(decimal.Decimal(lhs) / decimal.Decimal(1000000))

        real_lhs = parse_duration(lhs)

        if real_lhs is None:

            real_lhs = backend_utils.typecast_timestamp(lhs)

        if isinstance(rhs, int):

        if isinstance(rhs, six.integer_types):

            rhs = str(decimal.Decimal(rhs) / decimal.Decimal(1000000))

        real_rhs = parse_duration(rhs)

        if real_rhs is None: