I am interested in figuring out how to get the names and types of the columns from an arbitrary query. Essentially, I want to be able to take a query like:
CREATE TABLE foo(
SELECT * FROM foo WHERE bar = 42;
and figure out programmatically that the select will return a column "bar" of type bigserial, and a column "foo" of type varchar(256). I would like this to work for more complex queries as well (joins, CTEs, etc).
I've found https://wiki.postgresql.org/wiki/Query_Parsing, which talks about related ways to hook into postgres, but that seems to only talk about the parse tree — a lot more detail and processing seems to be required in order to figure out the output types. It seems like there should be somewhere I can hook into in postgres that will get me this information, but I have no familiarity with the codebase, so I don't know the best way to get this.
How would you recommend that I approach this? I'm comfortable patching postgres if needed, although if there's a solution that doesn't require that, I'd prefer that.
I'm writing some code that takes a given query, and generates type-safe bindings for it, so people can write SQL queries and get structs (or vectors of structs) out the other end. So I'm pretty flexible about where I get it, given that it'll be part of my build/codegen process. I hadn't seen libpq yet, I'll look into that — thanks!