Prova detta:
select a.id,a.user,a.item_id,a.created
from reports as a
where a.created=(select max(created)
from reports as b
where a.item_id=b.item_id)
Prova detta:
select a.id,a.user,a.item_id,a.created
from reports as a
where a.created=(select max(created)
from reports as b
where a.item_id=b.item_id)