Having borde väl funka:
Kod:
select first_name, last_name, count(*) as cnt
from table
group by first_name, last_name
having cnt > 1
Alternativt:
Kod:
select distinct t1.first_name, t1.last_name
from table t1, table t2
where t1.id != t2.id
and t1.first_name = t2.first_name
and t1.last_name = t2.last_name