SELECT SYSDATE-1 FROM DUAL;  --减一天  
SELECT TO_DATE('2014-06-10 12:05:22','YYYY-MM-DD HH24:MI:SS')-NUMTODSINTERVAL(1,'HOUR') FROM DUAL;--减一小时  
SELECT TO_DATE('2014-06-10 12:05:22','YYYY-MM-DD HH24:MI:SS')+NUMTODSINTERVAL(1,'HOUR') FROM DUAL;--加一小时  
SELECT SYSDATE, SYSDATE+NUMTODSINTERVAL(50,'MINUTE') FROM DUAL ; --加五十分钟  
  
SELECT SYSDATE, SYSDATE+NUMTODSINTERVAL(1,'HOUR') FROM DUAL ; --加一小时  
SELECT SYSDATE, SYSDATE+NUMTODSINTERVAL(45,'SECOND') FROM DUAL ; --加45秒  
SELECT SYSDATE, ADD_MONTHS(SYSDATE,12*2) FROM DUAL ; -- 当前日期增加两年