select 
      t.dt "日期",
      --环比
      (
           ------------分子---------------
         (   t.cnt-
            (select t1.cnt
            from t1
            where to_char(t1.dt,'yyyy-mm-dd') = to_char(add_months(trunc(t.dt),-1),'yyyy-mm-dd') --上月数据
            )
         ) / 
         ------------分母---------------
         (select t1.cnt
            from t t1
            where to_char(t1.dt,'yyyy-mm-dd') = to_char(add_months(trunc(t.dt),-1),'yyyy-mm-dd')
          )
      )*100 || '%' as "环比增长率"
from
       t t
where to_char(t.dt,'yyyy-mm-dd')='2012-02-01'