mysql如何查询子节点

select id from (

              select t1.id,

              if(find_in_set(parent_id, @pids) > 0, @pids := concat(@pids, ',', id), 0) as ischild

              from (

                   select id,parent_id from re_menu t where t.status = 1 order by parent_id, id

                  ) t1,

                  (select @pids := 要查询的菜单节点 id) t2

             ) t3 where ischild != 0