SQL::
Updating the column with value as D when it is duplicated.

Please go through the process.............................!

create table Emp_testing as select * from emp;//Creating the Table

select * from Emp_testing;

insert into Emp_testing values('7369','SMITH','CLERK','7902','17-DEC-80','800','','20');                          
insert into Emp_testing values('7369','SMITH','CLERK','7902','17-DEC-80','800','','20');
insert into Emp_testing values('7369','SMITH','CLERK','7902','17-DEC-80','800','','20');
 insert into Emp_testing values('7369','SMITH','CLERK','7902','17-DEC-80','800','','20');
commit;

alter table Emp_testing add status varchar2(4);

select empno,ename,job,mgr,hiredate,sal,comm,deptno,status,count(1) as counts
from Emp_testing group by empno,ename,job,mgr,hiredate,sal,comm,deptno,status;

UPDATE Emp_testing t2
    SET t2.status = 'D'
    WHERE t2.rowid > (SELECT min(t1.rowid)
                    FROM Emp_testing t1
                    WHERE t1.ename=t2.ename);

you will the output in Status  column with D value it indicates that Those are duplicates