PostgreSQL - RETURNING INTO array - function

Question

I want to store an update's RETURNING values into a data structure so that I can use it in a subsequent query.
In this example, I'm given a list of "parent_ids", and I want to find all children whose parent is in that array. Then, I wish to update some value on them, and do other stuff.
CREATE OR REPLACE FUNCTION plpgsql_is_really_great(parent_ids bigint[])
RETURNS void AS
$$
DECLARE
found_ids bigint[];
BEGIN
UPDATE child SET
foo = bar
FROM
(SELECT id
FROM child
WHERE parent_id=ANY(parent_ids)
) as children_ids
WHERE
child.id = children_ids.id
RETURNING children_ids.id INTO found_ids; -- ???
-- do more stuff with found_ids
$$ LANGUAGE plpgsql

Answer 1

There are a few ways to go about this.
Say you want to call some f(id) for each id affected by the UPDATE.
In PL/pgSQL:
$$
DECLARE found_id BIGINT;
BEGIN
FOR found_id IN (UPDATE child SET foo=bar RETURNING id) LOOP
PERFORM f(found_id);
END LOOP;
END
$$
In pure SQL:
WITH updated(found_id) AS (
UPDATE child SET foo=bar RETURNING id
)
SELECT f(found_id) FROM updated;
If you want to collect all the found_ids in an array, you can simply:
$$
DECLARE array_var BIGINT[];
BEGIN
WITH updated(found_id) AS (
UPDATE child SET foo=bar RETURNING id
)
SELECT array_agg(found_id) FROM updated INTO array_var;
END
$$

Answer 2

Here is an example:
CREATE OR REPLACE FUNCTION exemplary ( parent_ids bigint[] )
RETURNS VOID AS $$
DECLARE
_found_ids bigint[];
BEGIN
WITH matching_children AS (
UPDATE child
SET foo = 1
WHERE parent_id = ANY ( parent_ids )
RETURNING id
)
SELECT array_agg ( id )
FROM matching_children
INTO _found_ids;
RAISE NOTICE '%', _found_ids;
RETURN;
END $$ LANGUAGE plpgsql;