Comments - Recursive Common Table Expressions Overview

Sorry that the formatting was not maintained in the reply above.

From an example in the documentation above, I've added n, which represents the level within the hierarchy:

CREATE TABLE bus_routes (origin varchar(50), dst varchar(50));
INSERT INTO bus_routes VALUES
 ('New York', 'Boston'),
 ('Boston', 'New York'),
 ('New York', 'Washington'),
 ('Washington', 'Boston'),
 ('Washington', 'Raleigh')
;

WITH RECURSIVE paths (n, cur_path, cur_dest) AS (
 SELECT 1 AS n, origin, origin
   FROM bus_routes
  WHERE origin='New York'
  UNION
 SELECT n + 1, CONCAT(paths.cur_path, ',', bus_routes.dst), bus_routes.dst
   FROM paths, bus_routes
  WHERE paths.cur_dest = bus_routes.origin
    AND LOCATE(bus_routes.dst, paths.cur_path) = 0
 )
SELECT * FROM paths;