--시퀀스생성
CREATE SEQUENCE SEQ_HAHA
  START WITH 1
  MAXVALUE 33696
  MINVALUE 1
  CYCLE
  CACHE 10
  ORDER;
 
 
--펑션생성
CREATE OR REPLACE FUNCTION FUNC_HAHA RETURN VARCHAR2 IS
SEQ_ID NUMBER;
VAR_RTN VARCHAR2(3);
BEGIN
        SELECT TO_CHAR(SEQ_HAHA.NEXTVAL) INTO SEQ_ID FROM DUAL;
       
        IF SEQ_ID < 1000 THEN
            SELECT LPAD(SEQ_ID, 3, '0') INTO VAR_RTN FROM DUAL;
        ELSE
            SELECT DECODE(MOD(CEIL((TO_NUMBER(SEQ_ID)-999) / 36 /36), 26),1,'A',2,'B',3,'C',4,'D',5,'E',6,'F',7,'G',8,'H',9,'I',10,'J',11,'K',12,'L',13,'M',14,'N',15,'O',16,'P',17,'Q',18,'R',19,'S',20,'T',21,'U',22,'V',23,'W',24,'X',25,'Y',0,'Z')
                ||DECODE(MOD(CEIL(((TO_NUMBER(SEQ_ID)-999) /36)),36),1,'0',2,'1',3,'2',4,'3',5,'4',6,'5',7,'6',8,'7',9,'8',10,'9',11,'A',12,'B',13,'C',14,'D',15,'E',16,'F',17,'G',18,'H',19,'I',20,'J',21,'K',22,'L',23,'M',24,'N',25,'O',26,'P',27,'Q',28,'R',29,'S',30,'T',31,'U',32,'V',33,'W',34,'X',35,'Y',0,'Z')
                ||DECODE(MOD((TO_NUMBER(SEQ_ID)-999), 36),1,'0',2,'1',3,'2',4,'3',5,'4',6,'5',7,'6',8,'7',9,'8',10,'9',11,'A',12,'B',13,'C',14,'D',15,'E',16,'F',17,'G',18,'H',19,'I',20,'J',21,'K',22,'L',23,'M',24,'N',25,'O',26,'P',27,'Q',28,'R',29,'S',30,'T',31,'U',32,'V',33,'W',34,'X',35,'Y',0,'Z') AS R_VAR
                INTO VAR_RTN
            FROM DUAL;
        END IF;

   RETURN VAR_RTN;
   EXCEPTION
     WHEN NO_DATA_FOUND THEN
       RETURN('');
     WHEN OTHERS THEN
       RETURN('');
END FUNC_HAHA;
/

--펑션 호출
SELECT FUNC_HAHA() FROM DUAL;

얼추 간단히 테스트는 해봤는데....

시퀀스랑 펑션 생성하셔서 이리저리 테스트 해보세요....

무한사랑 감사합니다 ^^