
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
if (!skip_not_null_check)
                {
                    const auto & col = arguments[0].column;
                    const auto & nullable_col = assert_cast<const ColumnNullable &>(*col);
                    const auto & null_map = nullable_col.getNullMapData();
                    if (!memoryIsZero(null_map.data(), 0, null_map.size()))
                        throw Exception{"Cannot convert NULL value to non-Nullable type",
                                        ErrorCodes::CANNOT_INSERT_NULL_IN_ORDINARY_COLUMN};
                }
                const ColumnNullable * nullable_source = typeid_cast<const ColumnNullable *>(arguments.front().column.get());
                return wrapper(tmp_args, nested_type, nullable_source, input_rows_count);
            };
        }
        else
            return wrapper;
    }
    
    
    WrapperType prepareImpl(const DataTypePtr & from_type, const DataTypePtr & to_type, bool requested_result_is_nullable) const
    {
        if (isUInt8(from_type) && isBool(to_type))
            return createUInt8ToBoolWrapper(from_type, to_type);
        
        bool safe_convert_custom_types = true;
        if (const auto * to_type_custom_name = to_type->getCustomName())
            safe_convert_custom_types = from_type->getCustomName() && from_type->getCustomName()->getName() == to_type_custom_name->getName();
        else if (const auto * from_type_custom_name = from_type->getCustomName())