http://frombtod.tistory.com/2

참조 해보세요..

WITH t AS
(
SELECT '01' a, 'T' b, '0100' c, 'T0000' id, '' pid, 'T첫번째' nm FROM dual
UNION ALL SELECT '01', 'T', '2100', 'T1000', ''     , 'T두번째' FROM dual
UNION ALL SELECT '01', 'L', '2100', 'L212I', ''     , 'L첫번째' FROM dual
UNION ALL SELECT '01', 'L', '2100', 'L212N', 'L212I', 'L두번째' FROM dual
UNION ALL SELECT '02', 'T', '3100', 'T3000', ''     , '020202' FROM dual
UNION ALL SELECT '02', 'T', '4100', 'T4000', ''     , '030303' FROM dual
UNION ALL SELECT '02', 'L', '3100', 'L3131', ''     , '02엘이다' FROM dual
UNION ALL SELECT '02', 'L', '3100', 'L313N', 'L3131', '02엘엘이다' FROM dual
UNION ALL SELECT '02', 'L', '3100', 'L31NN', 'L313N', '02엘엘엘이다' FROM dual
)
SELECT a, b, c, id, pid, nm
     , LEVEL lv
     , SYS_CONNECT_BY_PATH(nm, '>') pth
  FROM t
 START WITH b = 'T' AND pid IS NULL
 CONNECT BY PRIOR a = a
        AND PRIOR c = c
        AND (PRIOR id = pid OR (b = 'L' AND PRIOR b = 'T' AND pid IS NULL))
;