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;