CTE get all descendants with parents

Schema:
CREATE TABLE item (
id int primary key,
parent_id int,
FOREIGN KEY(parent_id) REFERENCES item(id)
);

INSERT INTO item
(id, parent_id)
VALUES
(1, NULL),
(2, 1),
(3, 1),
(4, 2),
(5, 3),
(6, 3),
(7, 6)
;


Query:
WITH RECURSIVE descendants(id, parent_id) AS (
SELECT 1, parent_id FROM item
UNION ALL
SELECT item.id, descendants.parent_id
FROM item, descendants
WHERE item.parent_id=descendants.id
)
SELECT * FROM descendants;


Fiddle: http://sqlfiddle.com/#!5/27c03/4

Goal: given some parents (eg 2, 3) get all of its descendants.

I came up with the following CTE, but it returns far too many items.

SELECT * FROM descendants WHERE parent_id IN (2, 3);

Should give

id | parent_id
4  | 2
5  | 3
6  | 3
7  | 3

The answer here is close, but my schema varies: https://dba.stackexchange.com/a/94944/253249

Please try and let me know if it helps :

WITH descendants as
(
  SELECT i.id, i.parent_id, CAST(i.id AS varchar) as Level
  FROM item i
  WHERE i.parent_id is null

  UNION ALL

  SELECT i1.id, i1.parent_id, CAST(i1.id AS varchar) || ', ' || d.Level
  FROM item i1  
  INNER JOIN descendants d ON d.id = i1.parent_id
 )
SELECT * 
From descendants
where parent_id in (2,3)

Demo

Reference

StackExchange Database Administrators Q#312724, answer score: 3