Prova detta:
select t1.* from attachments t1
left join attachments t2
on t1.entity_id = t2.entity_id and t1.group_id = t2.group_id and
t1.version_number < t2.version_number
where t2.version_number is null
Prova detta:
select t1.* from attachments t1
left join attachments t2
on t1.entity_id = t2.entity_id and t1.group_id = t2.group_id and
t1.version_number < t2.version_number
where t2.version_number is null