先对结果集排序然后做update、delete操作

--先排序然后删除第n条数据
delete from scott.emp
 where empno in (select empno
                   from (select *
                           from scott.emp
                          where comm is null
                            and rownum < 2
                          order by hiredate desc));

--先排序然后更新第n条数据
update scott.emp                                  
   set comm = 123                                 
 where empno in (select empno                     
                   from (select empno             
                           from scott.emp         
                          where rownum < 2        
                            and comm is null      
                          order by hiredate asc));