Hi Nikhil,
Can you please confirm which version of HANA are you using. Following SQL is working fine for me and I am on revision 52.
select PNODE, CNODE, CSTATUS, ROW_NUMBER() over (partition by PNODE order by CNODE) as "SS"
from T;
(My T Table has different structure, but still it works).
Regards,
Ravi