Rank only summary rows from group by rollup

Question

I would like to rank only the total rows generated by a group by rollup, but not rank the rows within each group by bucket. Furthermore, I'd like to order by rank in descending order and include the unranked rows within each group.
My query looks something like this:
select customer, month, sum (sell)
from sales
group by rollup (customer, month)
order by customer, month desc nulls first
The results look like:
customer     month     sum(sell)
<summary rowA>          1,200
custA          JAN     100
custA          FEB     100
custA          MAR     100
custA          DEC     100
<summary rowB>          600
custB          JAN     50
custB          FEB     50
custB          MAR     50
custB          DEC     50
What I would like to do is:
select dense_rank() over (order by sum(sell) desc <rollup rows only>) as rank,
     customer, month, sum (sell)
from sales
group by rollup (customer, month)
order by <summary row rank desc> customer, month desc nulls first
The results would look like:
rank     customer     month     sum(sell)
1     <summary rowA>          1,200
     custA          JAN     100
     custA          FEB     100
     custA          MAR     100
     custA          DEC     100
2     <summary rowB>          600
     custB          JAN     50
     custB          FEB     50
     custB          MAR     50
     custB          DEC     50
Any advice?
Thank you

Answer 1

Like this?
sql>
select decode(job,null,decode(deptno,null,null,dense_rank() over(order by lst desc)-1),null) rank,
       deptno,job,sm
from(
      select deptno,job,sm,last_value(sm) over(partition by deptno order by null ) lst
      from (
            select deptno,job,sum(sal) sm
            from emp
            group by rollup(deptno,job)));
RANK DEPTNO JOB SM
                   29025 
   20  CLERK  1900 
   20  MANAGER  2975 
1  20     10875 
   20  ANALYST  6000 
   30  CLERK  950 
   30  MANAGER  2850 
2  30     9400 
   30  SALESMAN  5600 
   10  CLERK  1300 
   10  MANAGER  2450 
   10  PRESIDENT  5000 
3  10     8750