SQL> select * from t1 ;

ID EFF_DATE
---------- ---------
100 05-JUL-03
100 08-AUG-03
100 10-SEP-03
200
300 08-MAY-01

SQL>
1 select id, max(eff_date) last_eff_date,
2 decode(max(eff_date), null,null , add_months(max(eff_date),24))
3 from t1
4* group by id;

ID LAST_EFF_ DECODE(MA
---------- --------- ---------
100 10-SEP-03 10-SEP-05
200
300 08-MAY-01 08-MAY-03

Is this you want?

Tamil