
select toDateTime64(-86400 ,9,'UTC') ==  1969-12-31 00:00:00.000000000

select toDateTime64(-86400.00 ,9,'UTC') ==  1970-01-01 00:00:00.000000000 


However, I expect both outputs to be same. 

Version affected : 22.8
vec_to[i] = value;
                    }
                    else if constexpr (IsDataTypeDecimal<ToDataType>)
                    {
                        SerializationDecimal<typename ToDataType::FieldType>::readText(
                            vec_to[i], read_buffer, ToDataType::maxPrecision(), col_to->getScale());
                    }
                    else
                    {
                        parseImpl<ToDataType>(vec_to[i], read_buffer, local_time_zone);
                    }
                }
                if (!isAllRead(read_buffer))
                    throwExceptionForIncompletelyParsedValue(read_buffer, *res_type);
            }
            else
            {
                bool parsed;
                if constexpr (parsing_mode == ConvertFromStringParsingMode::BestEffort)
                {
                    if constexpr (to_datetime64)
                    {
                        DateTime64 res = 0;
                        parsed = tryParseDateTime64BestEffort(res, col_to->getScale(), read_buffer, *local_time_zone, *utc_time_zone);
                        vec_to[i] = res;
                    }
                    else
                    {
                        time_t res;
                        parsed = tryParseDateTimeBestEffort(res, read_buffer, *local_time_zone, *utc_time_zone);