Rownumber   list
1           UK,DDN,HWR,RKE
2           UP,SRE,NGL,TPR



create table pp(Cid varchar2(30),PID varchar2(30));

insert into pp values('UP','');
insert into pp values('SRE','UP');
insert into pp values('TPR','SRE');
insert into pp values('NGL','SRE');
insert into pp values('UK','');
insert into pp values('HWR','UK');
insert into pp values('DDN','UK');
insert into pp values('RKE','HWR');
COMMIT;