Expand type support

[Mytherin]

• Floating point
• Decimals

[wuputah]

suggestions for further expansion (can create additional github issues):

• uuid
• json and jsonb
• arrays
• fallback to varchar

[Mytherin]

Longer term goal:

• Preserve Postgres types also in DuckDB
• Add a way of calling Postgres functions from within DuckDB, directly on the preserved types
• Ideally lazily/automatically register Postgres functions that DuckDB does not have inside DuckDB so they can be used (as a slower fallback)

[Tishj]

Longer term goal:

• Preserve Postgres types also in DuckDB
• Add a way of calling Postgres functions from within DuckDB, directly on the preserved types
• Ideally lazily/automatically register Postgres functions that DuckDB does not have inside DuckDB so they can be used (as a slower fallback)

I'm already (ab)using our type system to convey information between bind and postgres->duckdb value conversion like this:

		if (typmod == -1 || precision < 0 || scale < 0 || precision > 38) {
			auto extra_type_info = duckdb::make_shared<NumericAsDouble>();
			return duckdb::LogicalType(duckdb::LogicalTypeId::DOUBLE, std::move(extra_type_info));
		}

		if (aux_info && dynamic_cast<NumericAsDouble *>(aux_info.get())) {
			// This NUMERIC could not be converted to a DECIMAL, convert it as DOUBLE instead
			auto numeric = DatumGetNumeric(value);
			auto numeric_var = FromNumeric(numeric);
			auto double_val = ConvertDecimal<double, DecimalConversionDouble>(numeric_var);
			Append<double>(result, double_val, offset);
		}

We can probably use a similar method to preserve the postgres types

[Mytherin]

Instead of falling back to VARCHAR, let's add a custom type (UnsupportedPostgresType) that triggers an error when it gets used.

[wuputah]

this has been mostly addressed in #23; lets open a new issue for anything else we are looking to address