select MC,ZJBH,XZQ,SLRQ,SFHMD,DQSJ,
case when DQSJ is null or DQSJ-sysdate>45 then '正常'
when DQSJ-sysdate>0 and DQSJ-sysdate<=45 then '快到期'
when DQSJ-sysdate<=0 then '到期' end DQZT  
  from USER_ZGINFO

------解决方案--------------------

SQL code

create table t1(d_date date);

insert into t1 values (to_date('2012-06-01 12:00:00','yyyy-mm-dd hh24:mi:ss'));
insert into t1 values (to_date('2012-03-01 12:00:00','yyyy-mm-dd hh24:mi:ss'));
insert into t1 values (to_date('2012-04-01 12:00:00','yyyy-mm-dd hh24:mi:ss'));
insert into t1 values (to_date('2012-05-01 12:00:00','yyyy-mm-dd hh24:mi:ss'));


select d_date,
       case when d_date-sysdate>45 then '正常' 
            when d_date-sysdate<=45 and  d_date-sysdate>0 then '快到期'
            when d_date-sysdate<=0 then '到期' end d_state
from t1  

         d_date             d_state
---------------------------------------------
1    2012/6/1 12:00:00    正常
2    2012/3/1 12:00:00    到期
3    2012/4/1 12:00:00    快到期
4    2012/5/1 12:00:00    快到期