with t as (select 1 Contract,  'Вася' Name, 'USD' Currency from dual union all
select 1 Contract,  'Дима' Name, 'EUR' Currency from dual union all
select 1 Contract,  'Маша' Name, 'RUB' Currency from dual union all
select 2 Contract,  'Саша' Name, 'USD' Currency from dual)
select contract, max(ltrim(sys_connect_by_path(name,','), ',')), max(ltrim(sys_connect_by_path(currency,','), ','))
from
  (select t.*, row_number() over (partition by contract order by 1) rn from t) 
connect by rn-1 = prior rn and contract = prior contract
start with rn = 1
group by contract