Oracle如何获取数据库系统的当前时间

UPDATE MY_TABLE
 SET MODIFY_TIME = SYSDATE
 WHERE DELETED = 0
   AND ID = 'XXX'

SELECT NOW()

SELECT SYSDATE FROM DUAL

select extract(year from sysdate)　from dual; --当前年 

select extract(month from sysdate) from dual; --本年到当月的月数 

select extract(day from sysdate)　from dual; --本月到当日的天数 

select extract(year from date'2011-05-17') year from dual; 

select extract(month from date'2011-05-17') month from dual; 

select extract(day from date'2011-05-17') day from dual; 

select  to_char(sysdate, 'yyyy' )  from dual; --年 
   
select  to_char(sysdate, 'MM' )  from dual; --月 

select  to_char(sysdate, 'dd' )  from dual; --日 

select  to_char(sysdate,'Q')  from dual; --季 

select  to_char(sysdate,'iw')  from dual; --周--按日历上的那种，每年有52或者53周 

select sysdate,sysdate - interval '7' MINUTE from dual;

select sysdate - interval '7' hour from dual;

select sysdate - interval '7' day from dual;

select sysdate,sysdate - interval '7' month from dual;

select sysdate,sysdate - interval '7' year from dual;

select sysdate,sysdate - 8*interval '7' hour from dual;