Using PERFORM in recursive query function in PostgreSQL - postgresql

Question

I have a recursive query which I want to use in PostgreSQL function, and it should return a Boolean value.
CREATE OR REPLACE FUNCTION store.is_item(object1 VARCHAR(40), object2 VARCHAR(40))
RETURNS BOOLEAN AS $$
BEGIN
WITH RECURSIVE externals AS (
SELECT object_id, used_id
FROM store.obj_depend
WHERE external = true
), history AS (
SELECT content_id AS id
FROM store.minfos
WHERE id= $2
UNION
SELECT externals.used_id
FROM externals
INNER JOIN history ON history.id = externals.object_id
),
PERFORM (SELECT c.id FROM store.cinfo AS c WHERE c.id = $1 INNER JOIN history
ON c.id = history.id);
RETURN FOUND;
END;
$$ LANGUAGE plpgsql;
When I try this it gives asyntax error at or near SELECT error.

Answer 1

The PERFORM is plpgsql statement and cannot be used inside any SQL command.
You can use PERFORM like proposed #klin, but then CTE is used inside a subquery, and subquery returns one row every time. Then a FOUND variable should be every time true.
In this case is better to use auxiliary variable as targer:
CREATE OR REPLACE FUNCTION store.is_item(object1 VARCHAR(40), object2 VARCHAR(40))
RETURNS BOOLEAN AS $$
DECLARE r record;
BEGIN
WITH RECURSIVE
externals AS (SELECT object_id, used_id
FROM store.obj_depend
WHERE external = true)
history AS (SELECT content_id AS id
FROM store.minfos
WHERE id = object2
UNION
SELECT externals.used_id
FROM externals
INNER JOIN history ON history.id = externals.object_id)
SELECT c.id
FROM store.cinfo AS c
INNER JOIN history ON c.id = history.id
WHERE c.id = $1
INTO r;
RETURN FOUND;
END;
$$ LANGUAGE plpgsql;