gistfile1.rb

def subtree_ids_sql(depth)
    tree_sql =  <<-SQL
      WITH RECURSIVE search_tree(id, path, depth) AS (
          SELECT id, ARRAY[id], 1
          FROM users
          WHERE id = #{id}
        UNION ALL
          SELECT users.id, path || users.id, search_tree.depth + 1
          FROM search_tree
          JOIN users ON users.parent_id = search_tree.id
          WHERE NOT users.id = ANY(path) AND search_tree.depth <= #{depth}
      )
      SELECT id FROM search_tree where search_tree.id != #{id} ORDER BY path
    SQL
  end