MySQL recursive tree find

mysql_recursive_tree_find.sql

-- Variables to change
-- L13: menu (mysql table)
-- L14: id_menu (mysql table id)
-- L18: 304 (child id from where to start finding the root id)
-- @ref: https://explainextended.com/2009/07/20/hierarchical-data-in-mysql-parents-and-children-in-one-query/

SELECT  CONCAT(REPEAT('    ', level  - 1), CAST(_id AS CHAR)) AS treeitem,
        parent,
        level
FROM    (
        SELECT  @r AS _id,
                (
                SELECT  @r := parent_menu_id
                FROM    menu
                WHERE   id_menu = _id
                ) AS parent,
                @l := @l + 1 AS level
        FROM    (
                SELECT  @r := 304,
                        @l := 0
                ) vars,
                menu h
        WHERE   @r <> 0
        ) q