select decode(moduleid, rootmoduleid, sum) sum,
  moduleid, modulename, parentid, leaf, "level", orderid from
(select sum(1) over(partition by rootmoduleid) sum, t1.* from 
  (select t.*, connect_by_root moduleid rootmoduleid from t
    start with "level"=2 connect by prior moduleid=parentid) t1
order by rootmoduleid, parentid, orderid);

------解决方案--------------------

--moduleid modulename parentid leaf level orderid
WITH t AS
 (SELECT 1 AS mId,
   '菜单1'   AS mName,
   0       AS pid,
   1       AS leaf,
   2       AS lvl,
   1       AS orderid
 FROM dual
 UNION ALL
 SELECT 2, '菜单2', 0, 1, 2, 2 FROM dual
 UNION ALL
 SELECT 11, '菜单11', 0, 1, 2, 11 FROM dual
 UNION ALL
 SELECT 12, '菜单12', 1, 0, 3, 1 FROM dual
 UNION ALL
 SELECT 13, '菜单13', 1,1, 3, 1 FROM dual
 UNION ALL
 SELECT 14, '菜单14', 11, 1, 3, 1 FROM dual
 UNION ALL
 SELECT 215, '菜单215', 13, 1, 4, 1 FROM dual
 UNION ALL
 SELECT 216, '菜单216', 14, 0, 4, 1 FROM dual
 UNION ALL
 SELECT 217, '菜单217', 215, 0, 5, 1 FROM dual
 )
SELECT mid,
 mname,
 pid,
 leaf,
 lvl,
 orderid,
 DECODE(lvl,2,aa,0) AS "SUM"
FROM
 (SELECT mid,
   mname,
   pid,
   leaf,
   lvl,
   orderid,
   (SELECT COUNT(1)
   FROM t t1
     CONNECT BY prior t1.mid=t1.pid
     START WITH t1.mid      = a.mid
   ) AS aa
 FROM
   ( SELECT * FROM t CONNECT BY prior mid = pid START WITH pid = 0
   ) a
 )
MID                    MNAME     PID                    LEAF                   LVL                    ORDERID                SUM                   
---------------------- --------- ---------------------- ---------------------- ---------------------- ---------------------- ----------------------  
1                      菜单1     0                      1                      2                      1                      5                     
12                     菜单12    1                      0                      3                      1                      0                     
13                     菜单13    1                      1                      3                      1                      0                     
215