Re: Getting column names/types from select query?

[Wesley Aptekar-Cassels]

> Where do you need this information?

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!

Getting column names/types from select query?

[Wesley Aptekar-Cassels]

Hi all,

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(
bar bigserial,
baz varchar(256)
);

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.

Thanks,

:w