
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
struct ConvertImpl<DataTypeString, ToDataType, Name, ConvertDefaultBehaviorTag>
    : ConvertThroughParsing<DataTypeString, ToDataType, Name, ConvertFromStringExceptionMode::Throw, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeFixedString>)
struct ConvertImpl<DataTypeFixedString, ToDataType, Name, ConvertDefaultBehaviorTag>
    : ConvertThroughParsing<DataTypeFixedString, ToDataType, Name, ConvertFromStringExceptionMode::Throw, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeString>)
struct ConvertImpl<DataTypeString, ToDataType, Name, ConvertReturnNullOnErrorTag>
    : ConvertThroughParsing<DataTypeString, ToDataType, Name, ConvertFromStringExceptionMode::Null, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeFixedString>)
struct ConvertImpl<DataTypeFixedString, ToDataType, Name, ConvertReturnNullOnErrorTag>
    : ConvertThroughParsing<DataTypeFixedString, ToDataType, Name, ConvertFromStringExceptionMode::Null, ConvertFromStringParsingMode::Normal> {};
template <typename StringColumnType>
struct ConvertImplGenericFromString
{
    static ColumnPtr execute(ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, const ColumnNullable * column_nullable, size_t input_rows_count)
    {
        static_assert(std::is_same_v<StringColumnType, ColumnString> || std::is_same_v<StringColumnType, ColumnFixedString>,
                "Can be used only to parse from ColumnString or ColumnFixedString");
        const IColumn & column_from = *arguments[0].column;
        const IDataType & data_type_to = *result_type;
        auto res = data_type_to.createColumn();
        auto serialization = data_type_to.getDefaultSerialization();
        const auto * null_map = column_nullable ? &column_nullable->getNullMapData() : nullptr;
        executeImpl(column_from, *res, *serialization, input_rows_count, null_map, result_type.get());
        return res;
    }
    static void executeImpl(