SQL & PL/SQL

Hi all,

I want to do cumulative sum in scenario below. my DB version: 10.2.0
the table and data:

CREATE TABLE T (DT DATE, USR VARCHAR2(3));

Insert into T (DT,USR) values (to_date('2011-03-26','YYYY-MM-DD'),'a');
Insert into T (DT,USR) values (to_date('2011-03-26','YYYY-MM-DD'),'b');
Insert into T (DT,USR) values (to_date('2011-03-27','YYYY-MM-DD'),'b');
Insert into T (DT,USR) values (to_date('2011-03-27','YYYY-MM-DD'),'c');
Insert into T (DT,USR) values (to_date('2011-03-28','YYYY-MM-DD'),'c');
Insert into T (DT,USR) values (to_date('2011-03-28','YYYY-MM-DD'),'d');
Insert into T (DT,USR) values (to_date('2011-03-29','YYYY-MM-DD'),'d');
Insert into T (DT,USR) values (to_date('2011-03-29','YYYY-MM-DD'),'e');

the result I want is :

dt                        distinct user
-------------------------------------
2011-03-26  	2
2011-03-27  	3
2011-03-28  	4
2011-03-29  	5

the only query I came up with is as below and it looks clumsy.
So, I wonder if there is a better way to do it?

SELECT a.dt, COUNT(DISTINCT b.usr)
FROM
  (SELECT DISTINCT DT FROM T ) A,
  T B
WHERE A.DT>=b.dt
GROUP BY a.dt;

OVER() seems not work, because oracle doesn`t allow COUNT(DISTINCT) be used together with OVER(ORDER BY ).

correct me if I am wrong.

Thanks