뒷자리는 1자리 고정인가요?
B 에 ACC 가 두개인데? 하나는 AC 일 것 같네요.

WITH TA AS (
SELECT 'ABC_A' A_A FROM DUAL UNION ALL
SELECT 'ACC_A' A_A FROM DUAL UNION ALL
SELECT 'AC_A'  A_A FROM DUAL UNION ALL
SELECT 'BAC_A' A_A FROM DUAL UNION ALL
SELECT 'BAA_C' A_A FROM DUAL UNION ALL
SELECT 'CC_A'  A_A FROM DUAL
)
, 
TB AS (
SELECT 'ABC' B_A , '감자'   B_B,	'강원도' B_C FROM DUAL UNION ALL
SELECT 'ACC' B_A , '고구마' B_B,	'강원도' B_C FROM DUAL UNION ALL
SELECT 'ACC' B_A , '사과'   B_B,	'충청도' B_C FROM DUAL UNION ALL
SELECT 'BAC' B_A , '딸기'   B_B,	'충청도' B_C FROM DUAL UNION ALL
SELECT 'BAA' B_A , '포도'   B_B,	'서울  ' B_C FROM DUAL UNION ALL
SELECT 'CC'  B_A , '포도'   B_B,	'서울  ' B_C FROM DUAL
)

SELECT * FROM TA, TB
WHERE INSTR(TA.A_A, TB.B_A) > 0;

이렇게 하면 되지 않을까요?

WITH ta AS
(
SELECT 'ABC_A' a FROM dual
UNION ALL SELECT 'ACC_A' FROM dual
UNION ALL SELECT 'AC_A'  FROM dual
UNION ALL SELECT 'BAC_A' FROM dual
UNION ALL SELECT 'BAA_C' FROM dual
UNION ALL SELECT 'CC_A'  FROM dual
)
, tb AS
(
SELECT 'ABC' a, '감자' b, '강원도' c FROM dual
UNION ALL SELECT 'ACC', '고구마', '강원도' FROM dual
UNION ALL SELECT 'AC' , '사과'  , '충청도' FROM dual -- ACC가 중복이라 AC 로 바꿈.
UNION ALL SELECT 'BAC', '딸기'  , '충청도' FROM dual
UNION ALL SELECT 'BAA', '포도'  , '서울'   FROM dual
UNION ALL SELECT 'CC' , '포도'  , '서울'   FROM dual
)
SELECT *
  FROM ta a
     , tb b
-- WHERE a.a LIKE b.a || '_%'                      -- LIKE 오답
 WHERE a.a LIKE b.a || '#_%' ESCAPE '#'          -- ESCAPE
-- WHERE INSTR(a.a, b.a) = 1                       -- INSTR 오답
-- WHERE INSTR(a.a, b.a || '_') = 1                -- INSTR
-- WHERE SUBSTR(a.a, 1, INSTR(a.a, '_') - 1) = b.a -- 잘라서 비교
-- WHERE REGEXP_LIKE(a.a, '^' || b.a || '_.+')     -- 정규식
;