
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
{
        auto getter = [&] (const auto & args) { return getReturnTypeImplRemovedNullable(args); };
        auto res = getReturnTypeDefaultImplementationForNulls(arguments, getter);
        to_nullable = res->isNullable();
        checked_return_type = true;
        return res;
    }
    DataTypePtr getReturnTypeImplRemovedNullable(const ColumnsWithTypeAndName & arguments) const
    {
        FunctionArgumentDescriptors mandatory_args = {{"Value", nullptr, nullptr, nullptr}};
        FunctionArgumentDescriptors optional_args;
        if constexpr (to_decimal)
        {
            mandatory_args.push_back({"scale", &isNativeInteger<IDataType>, &isColumnConst, "const Integer"});
        }
        if (!to_decimal && isDateTime64<Name, ToDataType>(arguments))
        {
            mandatory_args.push_back({"scale", &isNativeInteger<IDataType>, &isColumnConst, "const Integer"});
        }