Support postgres types transparently in queries

[osawyerr]

Is your feature request related to a problem or challenge?

DataFusion doesn't support native postgres types. I just realised that postgres queries that use postgres types, like the ones below, fail when executed against DataFusion. For example, the query below fails because the int8 isn’t recognised.

select sum(col1)::int8 from foo_table;

Describe the solution you'd like

Would be useful if type alisases were automatically supported without the user having to re-write postgres queries - e.g. int8 -> bigint and int4 -> int, etc.

Describe alternatives you've considered

Other databases support type aliases, I don't know how easy it is to implement that in DataFusion - https://duckdb.org/docs/sql/data_types/overview

Additional context

No response

[alamb]

I think this would be very straightforward as long as the postgres type had a clear mapping to an Arrow type. For example int8 maps seemingly nicely to DataType::Int8

The mapping of SQL type to ArrowType is done here:

https://github.com/apache/arrow-datafusion/blob/49583bd5010282ca126e75100dce958aa346e5ee/datafusion/sql/src/planner.rs#L308-L400

cDataFusion CLI v27.0.0
❯ create table foo(x int8);
This feature is not implemented: Unsupported SQL type Custom(ObjectName([Ident { value: "int8", quote_style: None }]), [])

So we would just have to encode a listing of custom type names to arrow

[alamb]

I think this is a good first issue as it is a substantial potential positive impact and relatively low complexity (add type aliases, update docs, write some tests) and would be a good way for someone to get started with DataFusion

[Kikkon]

If the issue is not urgent I'm happy to take it, I think it's a good opportunity to learn about DataFusion 🤣

[comphead]

I think this would be very straightforward as long as the postgres type had a clear mapping to an Arrow type. For example int8 maps seemingly nicely to DataType::Int8

@alamb I'm not sure this is correct, as Int8 should map to BigInt, but in the example above it is SmallInt
https://www.postgresql.org/docs/current/datatype-numeric.html

[alamb]

Thank you @comphead -- you are right, INt8 seeme to mean 8 bytes in postgres (not 8 bits) so the correct mapping is probably more like DataType::Int64

Thank you for https://www.postgresql.org/docs/current/datatype-numeric.html which is the definitive reference

[drauschenbach]

It appears that this issue, as it is written up, is now resolved.

[alamb]

Thanks for checking @drauschenbach -- closing!