Create table T(
ID number,
Custname Varchar2(20),
AddressType CHAR(1)
)


Insert into T values (1, 'John', 'P');
Insert into T values (1, 'John', 'Q');

Insert into T values (2, 'Kumar', 'P');
Insert into T values (2, 'kumar', 'Q');


Insert into T values (3, 'Martin', 'Q');


Insert into T values (4, 'Dennis', 'P');
Insert into T values (4, 'Dennis', 'Q');


Insert into T values (5, 'Raj', 'Q');

SQL> SELECT ID, CUSTNAME, ADDRESSTYPE
  2    FROM (SELECT T.*,
  3                 ROW_NUMBER() OVER(PARTITION BY LOWER(CUSTNAME) ORDER BY ID) RN
  4            FROM T)
  5   WHERE RN = 1
  6   ORDER BY ID;
 
        ID CUSTNAME             ADDRESSTYPE
---------- -------------------- -----------
         1 John                 P
         2 Kumar                P
         3 Martin               Q
         4 Dennis               P
         5 Raj                  Q

select t2.* 
from 
(
    select t1.*, 
           row_number() 
             over (partition by t1.custname order by t1.addresstype asc) rn 
    from t t1
) t2 
where t2.rn = 1;


        ID CUSTNAME             A         RN
---------- -------------------- - ----------
         4 Dennis               P          1
         1 John                 P          1
         2 Kumar                P          1
         3 Martin               Q          1
         5 Raj                  Q          1
         2 kumar                Q          1

6 rows selected.

orclz> select id,custname,min(addresstype) from t group by id,custname order by id;

        ID CUSTNAME             M
---------- -------------------- -
         1 John                 P
         2 Kumar                P
         2 kumar                Q
         3 Martin               Q
         4 Dennis               P
         5 Raj                  Q

6 rows selected.

orclz>

Create table T(
ID number,
Custname Varchar2(20),
AddressType CHAR(1)
)

select * from T

Insert into T values (1, 'John', 'P');
Insert into T values (1, 'John', 'Q');
Insert into T values (1, 'John', 'R');

Insert into T values (2, 'kumar', 'P');
Insert into T values (2, 'kumar', 'Q');
Insert into T values (2, 'kumar', 'R');


Insert into T values (3, 'Martin', 'R');
Insert into T values (3, 'Martin', 'Q');


Insert into T values (4, 'Dennis', 'P');
Insert into T values (4, 'Dennis', 'Q');

Insert into T values (5, 'Raj', 'R');
Insert into T values (5, 'Raj', 'Q');