Oracle select random rows matching a join condition

My objective is simple, I have to create a temporary table with some random values from a employee table whenever the department is in some particular department (say 2). For the rest of departments I don't care the value, it can be NULL.

Currently I have the following :

create table test 
as 
select s.DEPTNAME, 
        cast (
             (case when s.DEPTID in (2) then 
                (SELECT a.ENAME FROM 
                   (SELECT b.ENAME, b.DEPTID FROM EMPLOYEE b 
                    WHERE b.DEPTID IS NOT NULL 
                    ORDER BY DBMS_RANDOM.VALUE) a 
                  WHERE     a.DEPTID = s.DEPTID  AND ROWNUM = 1 
                )
               END)
              AS number) "ENAME" from DEPARTMENT s;

But the main issue here is related to performance. For every department value in 2 we do a sort of EMPLOYEE table to get a single random ENAME. Is there a better way to do this ? I know sample might work but I want to achieve more randomness.