Concatenation of setof type or setof record

I use Postgresql 9.1 with Ubuntu 12.04.

In a plpgsql function I try to concatenate setof type returned from another function.

the type pair_id_value in question is created with create type pair_id_value as (id bigint, value integer);

the function that returns elementary setof pair_id_value (those that will be concatenated later) is this one:

create or replace function compute_pair_id_value(id bigint, value integer)
    returns setof pair_id_value
as $
    listResults = []
    for x in range(0,value+1):
        listResults.append({ "id": id, "value": x})
    return listResults
$
language plpython3u;

this straigth-forward plpython code should be good, for exemple the query: select * from compute_pair_id_value(1712437,2); returns nicely:

id            | value 
 ---------------+-----------
        1712437 |         0
        1712437 |         1
        1712437 |         2
 (3 rows)

this python function is fairly simple for now, for this example, but above all for my proof of concept. It will be more complex in the near future.

The problem arises when I try to concatenate all the result tables from multiples id.

create or replace function compute_all_pair_id_value(id_obj bigint)
    returns setof pair_id_value as $
declare
    pair pair_id_value;
begin
    for pair in (select compute_pair_id_value(t.id, t.obj_value) from my_obj as t where t.id = id_obj)
    loop
            return next pair;
    end loop;
    return; 
end; $ language plpgsql;

I receive the error: invalid input syntax for integer "(1712437,0)" as if it is no longer seen as a pair_id_value with two columns but as a tuple (1712437,0).

So I changed the output type of the function from setof pair_id_value to setof record... and if I execute this similar concatenation function:

```
create or replace function compute_all_pair_id_value(id_obj bigint)
returns setof record as $$
declare
pair record;
begin
for pair in (select compute_pair_id_value(t.

The approach you're using is unnecessarily complex - and very inefficient. Instead of the first function use:

create or replace function compute_pair_id_value(id bigint, value integer)
    returns setof pair_id_value
as $
SELECT $1, generate_series(0,$2);
$                          
language sql;

or better, get rid of it entirely and write the whole operation like this:

-- Sample data creation:
CREATE TABLE my_obj(id bigint, obj_value integer);
insert into my_obj(id,obj_value) VALUES (1712437,2),(17000,5);

-- and the query:
SELECT id, generate_series(0,obj_value) FROM my_obj;

Resulting in:

regress=> SELECT id, generate_series(0,obj_value) FROM my_obj;
   id    | generate_series 
---------+-----------------
 1712437 |               0
 1712437 |               1
 1712437 |               2
   17000 |               0
   17000 |               1
   17000 |               2
   17000 |               3
   17000 |               4
   17000 |               5
(9 rows)

This exploits PostgreSQL's behaviour with set-returning functions called in the SELECT list. Once PostgreSQL 9.3 comes out it can be replaced with a standards-compliant LATERAL query.

Since it turns out your question was a simplified version of the real problem, let's tackle that. I'll work with the simplified compute_pair_id_value above to avoid the hassle of plpython3. Here's how to do what you want:

SELECT (compute_pair_id_value(id,obj_value)).* FROM my_obj;

Result:

regress=> SELECT (compute_pair_id_value(id,obj_value)).* FROM my_obj;
   id    | value 
---------+-------
 1712437 |     0
 1712437 |     1
 1712437 |     2
   17000 |     0
   17000 |     1
   17000 |     2
   17000 |     3
   17000 |     4
   17000 |     5
(9 rows)

but again, be warned that compute_pair_id_value will be called more than once. This is a limitation of PostgreSQL's query executor that can be avoided in 9.3 with LATERAL support, but as far as I know you're stuck with it in 9.2 and below. Observe:

create or replace function compute_pair_id_value(id bigint, value integer)
    returns setof pair_id_value
as $
BEGIN
  RAISE NOTICE 'compute_pair_id_value(%,%)',id,value;
  RETURN QUERY SELECT $1, generate_series(0,$2);
END;
$             
language plpgsql;

output:

regress=> SELECT (compute_pair_id_value(id,obj_value)).* FROM my_obj;
NOTICE:  compute_pair_id_value(1712437,2)
NOTICE:  compute_pair_id_value(1712437,2)
NOTICE:  compute_pair_id_value(17000,5)
NOTICE:  compute_pair_id_value(17000,5)
   id    | value 
---------+-------
 1712437 |     0
 1712437 |     1
 1712437 |     2
   17000 |     0
   17000 |     1
   17000 |     2
   17000 |     3
   17000 |     4
   17000 |     5
(9 rows)

See how compute_pair_id_value is called once per output column?

There is a workaround: Another layer of subquery to unpack the composite type result. See:

regress=> SELECT (val).* FROM (SELECT compute_pair_id_value(id,obj_value) FROM my_obj) x(val);
NOTICE:  compute_pair_id_value(1712437,2)
NOTICE:  compute_pair_id_value(17000,5)
   id    | value 
---------+-------
 1712437 |     0
 1712437 |     1
 1712437 |     2
   17000 |     0
   17000 |     1
   17000 |     2
   17000 |     3
   17000 |     4
   17000 |     5
(9 rows)

You can use the same technique in your code if you really must LOOP over the results (it's slow to do that, so avoid it if you can).

StackExchange Database Administrators Q#37547, answer score: 4