with a (id, name) as (values 
  ( 1 , 'Иванов')
, ( 1 , 'Иванов')
, ( 2 , 'Петров')
, ( 2 , 'Сидоров')
)
, b (id, name, rn) as (
select id, name, rownumber() over(partition by id) rn
from a
)
, c (id, name, rn) as (
select id, cast(name as varchar( 128 )) name, rn
from b
where rn= 1 
  union all
select b.id, c.name||';'||b.name, b.rn
from b, c
where b.id=c.id and b.rn=c.rn+ 1 
)
select c.id, c.name
from c
join (
select id, max(rn) rn from c group by id
) g (id, rn) on g.id=c.id and g.rn=c.rn