1. 날짜 ~ 시간 ('SECOND' , 'MINUTE', 'HOUR', 'DAY' )

SELECT TO_CHAR(SYSDATE + NUMTODSINTERVAL(2, 'HOUR'), 'YYYY-MM-DD HH24:MI:SS') FROM DUAL;

2. 년 ~ 월 ('YEAR', 'MONTH' )

SELECT  TO_CHAR(SYSDATE + NUMTOYMINTERVAL(2, 'MONTH'), 'YYYY-MM-DD HH24:MI:SS')
        TO_CHAR(ADD_MONTHS(SYSDATE, 2), 'YYYY-MM-DD HH24:MI:SS')
FROM DUAL;

SELECT TO_CHAR(SYSDATE + 1, 'YYYY-MM-DD HH24:MI:SS') FROM DUAL;

3. 시간차를 구하고 일시분초로 변환

SELECT  TO_CHAR(SYSDATE, 'YYYY-MM-DD HH24:MI:SS')                                               AS NOW
,       TRUNC(SYSDATE - TO_DATE('20140623080000', 'YYYYMMDDHH24MISS'))                          AS DD
,       TRUNC(MOD((SYSDATE - TO_DATE('20140623080000', 'YYYYMMDDHH24MISS')), 1) * 24)           AS HH24
,       TRUNC(MOD((SYSDATE - TO_DATE('20140623080000', 'YYYYMMDDHH24MISS')) * 24, 1) * 60)      AS MI
,       TRUNC(MOD((SYSDATE - TO_DATE('20140623080000', 'YYYYMMDDHH24MISS')) * 24 * 60, 1) * 60) AS SS
,       MONTHS_BETWEEN(TO_DATE('201707', 'YYYYMM'), TO_DATE('201701', 'YYYYMM'))                AS MM
FROM DUAL;

4. 시간계산

SELECT  TO_CHAR(SYSDATE, 'YYYY/MM/DD HH24:MI:SS')                           AS "현재시간"

,       TO_CHAR(SYSDATE - 1 / 24, 'YYYY/MM/DD HH24:MI:SS')                  AS "1시간 전"
,       TO_CHAR(SYSDATE - 60 / (24 * 60), 'YYYY/MM/DD HH24:MI:SS')          AS "60분 전"
,       TO_CHAR(SYSDATE - 30 / (24 * 60 * 60), 'YYYY/MM/DD HH24:MI:SS')     AS "30초 전"

,       TO_CHAR(SYSDATE + 1 / 24, 'YYYY/MM/DD HH24:MI:SS')                  AS "1시간 후"
,       TO_CHAR(SYSDATE + 60 / (24 * 60), 'YYYY/MM/DD HH24:MI:SS')          AS "60분 후"
,       TO_CHAR(SYSDATE + 30 / (24 * 60 * 60), 'YYYY/MM/DD HH24:MI:SS')     AS "30초 후"

,       TO_CHAR(SYSDATE + 1 / (24 * 60), 'YYYY/MM/DD HH24:MI:SS')           AS "1분 후"
,       TO_CHAR(SYSDATE + 1 / 24 / 60, 'YYYY/MM/DD HH24:MI:SS')             AS "1분 후"

,       TO_CHAR(TRUNC(SYSDATE) + 1 + 1 / 24, 'YYYY/MM/DD HH24:MI:SS')       AS "내일 오전 1시"  
,       TO_CHAR(TRUNC(SYSDATE) + 23 / 24, 'YYYY/MM/DD HH24:MI:SS')          AS "오늘 오후 11시" 
FROM DUAL;