with t as
(select 1 as grp, 11 as grp_detail, 't' as detail_mark from dual
 union all
 select 1 as grp, 12 as grp_detail, 't' as detail_mark from dual
 union all
 select 1 as grp, 13 as grp_detail, 't' as detail_mark from dual
 union all
 select 2 as grp, 21 as grp_detail, 'f' as detail_mark from dual
 union all
 select 2 as grp, 22 as grp_detail, 't' as detail_mark from dual
 union all
 select 2 as grp, 23 as grp_detail, 'f' as detail_mark from dual)
select *
from (
select grp
  , count(grp_detail) as qty
  , count(case when detail_mark = 't' then grp_detail else null end) as qty_is_mark
from t
group by grp)
where qty_is_mark = qty

where t.detail_mark = 't'
and not exists (select null from t t1 where t1.grp = t.grp and t1.detail_mark = 'f')