Oracle 日期处理

今年：select extract(year from sysdate) from dual;
今月：select extract(month from sysdate) from dual;
今日：select extract(day from sysdate) from dual;
      select trunc(sysdate,'dd') from dual;
今时：select trunc(sysdate,'hh24') from dual;
今分：select trunc(sysdate,'mi') from dual;


本月第一天：select trunc(sysdate,'month') from dual;
本月最后一天：select last_day(sysdate) from dual;

本周第一天：select trunc(sysdate,'day')+1 from dual;
本周最后一天：select trunc(sysdate,'day')+7 from dual;