WITH t AS
(
SELECT 'ABC' str FROM dual
UNION ALL SELECT 'ANBC' FROM dual
)
SELECT str
     , SUBSTR(str, 2, LENGTH(str) - 2) v
     , REGEXP_REPLACE(str, '^.|.$') v
  FROM t
;

WITH t AS
(
SELECT 'ABC' str FROM dual
UNION ALL
SELECT 'ANBC' FROM dual
UNION ALL
SELECT 'AC' FROM dual
)
SELECT  str
                 ,SUBSTR(str,INSTR(str, 'A') + 1,INSTR(str, 'C') - (INSTR(str, 'A') + 1))
  FROM  t
;
 

두분 모두 감사합니다

instr으로 좌표를 구해서 그 차를 이용해서 해결 하였습니다.

감사합니다!!^_^