http://justcramer.com/2010/05/30/scaling-threaded-comments-on-django-at-disqus/

	        
create table comments (
    id SERIAL PRIMARY KEY,
    message VARCHAR,
    author VARCHAR,
    parent_id INTEGER REFERENCES comments(id)
);
insert into comments (message, author, parent_id)
    values ('This thread is really cool!', 'David', NULL), ('Ya David, we love it!', 'Jason', 1), ('I agree David!', 'Daniel', 1), ('gift Jason', 'Anton', 2),
    ('Very interesting post!', 'thedz', NULL), ('You sir, are wrong', 'Chris', 5), ('Agreed', 'G', 5), ('Fo sho, Yall', 'Mac', 5);
			
	        

			
WITH RECURSIVE cte (id, message, author, path, parent_id, depth)  AS (
    SELECT  id,
        message,
        author,
        array[id] AS path,
        parent_id,
        1 AS depth
    FROM    comments
    WHERE   parent_id IS NULL

    UNION ALL

    SELECT  comments.id,
        comments.message,
        comments.author,
        cte.path || comments.id,
        comments.parent_id,
        cte.depth + 1 AS depth
    FROM    comments
    JOIN cte ON comments.parent_id = cte.id
    )
    SELECT id, message, author, path, depth FROM cte ORDER BY path;
	    	
			

输出结果

 id |           message           | author |  path   | depth
----+-----------------------------+--------+---------+-------
  1 | This thread is really cool! | David  | {1}     |     1
  2 | Ya David, we love it!       | Jason  | {1,2}   |     2
  4 | gift Jason                  | Anton  | {1,2,4} |     3
  3 | I agree David!              | Daniel | {1,3}   |     2
  5 | Very interesting post!      | thedz  | {5}     |     1
  6 | You sir, are wrong          | Chris  | {5,6}   |     2
  7 | Agreed                      | G      | {5,7}   |     2
  8 | Fo sho, Yall                | Mac    | {5,8}   |     2
(8 rows)