被SELECT语句难住了

In Oracle.table_test:
ID         ID_PRE     ID_NEXT
---------- ---------- ----------
01                    02
02         01         03
05         04         06
03         02         04
04         03         05>>SQL> SELECT id_pre,id,id_next
  2      FROM table_test
  3      START WITH id = '01' 
  4      CONNECT BY PRIOR id_next = id;ID_PRE     ID         ID_NEXT
---------- ---------- ----------
           01         02
01         02         03
02         03         04
03         04         05
04         05         06