Hugeint: SUM functions return tuples

[mpope9]

Thanks for the library! I'm seeing odd behaviour when using SUM functions, tuples are returned. They always seem to start with 0 as well.

Duckdbex.fetch_all("SELECT SUM(1);")
> [[{0, 1}]]

This doesn't happen with MAX:

Duckdbex.fetch_all("SELECT MAX(1);")
> [[1]]

[03juan]

It seems duckdb preemptively casts a SUM(param::INT) to a (signed) int128 HUGEINT.

https://github.com/duckdb/duckdb/blob/0024e5d4beba0185733df68642775e3f38e089cb/extension/core_functions/aggregate/distributive/sum.cpp#L31

which is represented as a tuple of signed and unsigned 64bit integers, {int64, uint64}.

duckdbex/c_src/value_to_term.cpp

Lines 95 to 102 in d6484a6

	case duckdb::LogicalTypeId::HUGEINT: {
	duckdb::hugeint_t hugeint = duckdb::HugeIntValue::Get(value);
	sink = enif_make_tuple2(env,
	enif_make_int64(env, hugeint.upper),
	enif_make_uint64(env, hugeint.lower)
	);
	return true;
	}

[AlexR2D2]

It seems duckdb preemptively casts a SUM(param::INT) to a (signed) int128 HUGEINT.

looks like you are right

so, i think, if you are expecting an integer number but got tuple/2 you can try this 'workaround'

iex > {:ok, res_ref} = Duckdbex.query(conn, "SELECT SUM(1);")
iex > [[res]] = Duckdbex.fetch_all(res_ref)
[[{0, 1}]]
iex [Вс :: 14] > Duckdbex.hugeint_to_integer(res)
1

[mpope9]

Neat! I think that workaround is good with me. Might be worth adding that as an example to the readme? Right now I'm just iterating over every cell and stripping the tuple.

[03juan]

@AlexR2D2 I came across various issues in other language's libraries using duckdb, where people are confused and surprised by this behaviour.

Since Erlang natively support arbitrary size integers, would you consider automatically converting these for the user?

I understand that you would want to maintain feature parity but maybe it can live behind a config flag and function opts.