时间常用的表达

1. 当月、下月等的取法
   当月：    to_char(sysdate, 'YYYYMM')
   下月：    to_char(add_months(sysdate, 1), 'YYYYMM')
   下下月：  to_char(add_months(sysdate, 2), 'YYYYMM')
   下下下月：to_char(add_months(sysdate, 3), 'YYYYMM')
   
2. 显示时分秒
   select to_date('2005-01-01 13:14:20','yyyy-MM-dd HH24:mi:ss') from dual;
   
3. --得到两个时间段的分钟之差
   select tt.reportdateMonth,
          abs((TO_DATE(to_CHAR(tt.reportdate, 'yyyyMMdd HH24:mi:ss'),
                       'YYYYMMDD HH24:MI:SS') -
              TO_DATE(to_CHAR(tt.createtime, 'yyyyMMdd HH24:mi:ss'),
                       'YYYYMMDD HH24:MI:SS')) * 24 * 60)
     from (select g.registno,
                  to_char(g.reportdate, 'mm') reportdateMonth,
                  g.reportdate,
                  (select max(r.createtime)
                     from r_message r
                    where r.registno = g.registno
                      and r.targettype = '1') createtime
             from gpregistcar g
            where g.lpflag = '0'
              and trunc(g.reportdate) between
                  to_date('2013-11-01', 'yyyy-mm-dd') and
                  to_date('2014-03-31', 'yyyy-mm-dd')) tt