Thread: Re: How to return seto records from seof record function?
On Tue, 2025-02-25 at 17:15 +0300, Олег Самойлов wrote:
> Postgresql 17.2
>
> How to return seto records from seof record function? I tried pg_background extension:
>
> CREATE OR REPLACE FUNCTION public.autonomous (p_script text)
> RETURNS SETOF record
> LANGUAGE plpgsql
> VOLATILE STRICT PARALLEL UNSAFE
> AS $autonomous$
> DECLARE
> l_id integer;
> BEGIN
> l_id := pg_background_launch(p_script);
> RETURN QUERY SELECT * FROM pg_background_result(l_id) AS (r record);
> END;
> $autonomous$;
>
> SELECT * FROM autonomous('SELECT now()') AS (a timestamptz);
>
> SQL Error [42804]: ERROR: structure of query does not match function result type
> Detail: Returned type record does not match expected type timestamp with time zone in column 1.
> Where: SQL statement "SELECT * FROM pg_background_result(l_id) AS (r record)"
> PL/pgSQL function autonomous(text) line 6 at RETURN QUERY
You need to be specific:
SELECT * FROM pg_background_result(l_id) AS (col1 integer, col2 text, ...);
I don't think there is a way to get a generic "record" as result.
And even if you could, you would still have to specify a column list
when you call autonomous().
Attempts to write functions with polymorphic return type are usually futile.
Perhaps you can return a "SETOF jsonb"...
Yours,
Laurenz Albe
Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Tue, 2025-02-25 at 17:15 +0300, Олег Самойлов wrote:
>> How to return seto records from seof record function? I tried pg_background extension:
> You need to be specific:
> SELECT * FROM pg_background_result(l_id) AS (col1 integer, col2 text, ...);
> I don't think there is a way to get a generic "record" as result.
> And even if you could, you would still have to specify a column list
> when you call autonomous().
plpgsql is indeed not too friendly to this, but perhaps a SQL-language
function would serve. That infrastructure seems to be okay with
wrapping a generic setof-record result:
regression=# \sf array_to_set
CREATE OR REPLACE FUNCTION public.array_to_set(anyarray)
RETURNS SETOF record
LANGUAGE sql
IMMUTABLE
AS $function$
select i AS "index", $1[i] AS "value" from generate_subscripts($1, 1) i
$function$
regression=# create or replace function wrapper(anyarray)
RETURNS SETOF record LANGUAGE sql as
$$ select 1; select array_to_set($1); $$;
CREATE FUNCTION
regression=# select wrapper(array[44,55,66]);
wrapper
---------
(1,44)
(2,55)
(3,66)
(3 rows)
regards, tom lane
On Tue, Feb 25, 2025 at 8:47 AM Laurenz Albe <laurenz.albe@cybertec.at> wrote:
I don't think there is a way to get a generic "record" as result.
And even if you could, you would still have to specify a column list
when you call autonomous().
Attempts to write functions with polymorphic return type are usually futile.
Perhaps you can return a "SETOF jsonb"...
There is only one non-jsonb method I'm aware of to convert string query to result without specifying result structure, and that's via refcursors, something like:
begin;
BEGIN;
CREATE FUNCTION f() RETURNS TEXT AS
$$
DECLARE
r REFCURSOR DEFAULT 'test';
BEGIN
OPEN r FOR EXECUTE $z$SELECT 'a' AS a, 1 AS b$z$;
RETURN r;
END;
$$ LANGUAGE PLPGSQL;
SELECT f();
FETCH test;
...
..I doubt it works in OP's case though as this only works to push all the way back to the client app. but it's a neat artifact from yore.
In modern postgres, I think jsonb is the way to go. Function output syntax is one of the clunkiest parts of the language, you are on a freight train to deep dynamic SQL; it sure would be nice if we could somehow pass an output definition somehow in a way the calling function or query could use. This mostly comes up in my experience with analytics, where the column needs are very dynamic and layered.
merlin