[sql] SQL not a single-group group function

When I run the following SQL statement:

SELECT MAX(SUM(TIME))
FROM downloads
GROUP BY SSN

It returns the maximum sum value of downloads by a customer, however if I try to find the social security number that that max value belongs to by adding it to the select statement:

SELECT SSN, MAX(SUM(TIME))
FROM downloads
GROUP BY SSN

I get the following error:

not a single-group group function

I do not understand why it is throwing this error. A google search came up with the following action:

Drop either the group function or the individual column expression from the SELECT list or add a GROUP BY clause that includes all individual column expressions listed

From what I think this is saying - dropping the group function makes the sum value invalid - droping the individual column expression (SSN) will just give me the max sum - not sure about that third part.

Could anyone guide in the right direction?

-Tomek

EDIT: TIME in this database refers to the number of times downloaded

Maybe you find this simpler

select * from (
    select ssn, sum(time) from downloads
    group by ssn
    order by sum(time) desc
) where rownum <= 10 --top 10 downloaders

Regards
K

If you want downloads number for each customer, use:

select ssn
     , sum(time)
  from downloads
 group by ssn

If you want just one record -- for a customer with highest number of downloads -- use:

select *
  from (
        select ssn
             , sum(time)
          from downloads
         group by ssn
         order by sum(time) desc
       )
 where rownum = 1

However if you want to see all customers with the same number of downloads, which share the highest position, use:

select *
  from (
        select ssn
             , sum(time)
             , dense_rank() over (order by sum(time) desc) r
          from downloads
         group by ssn
       )
 where r = 1