with test_data (grp, val) as (
    select 1, 8 from rdb$database
    union all
    select 1, 9 from rdb$database
    union all
    select 2, 3 from rdb$database
    union all
    select 2, 4 from rdb$database
)
select 
    grp,
    val,
    sum(val) over(partition by grp order by val) as s1,
    sum(val) over(w2) as s2
from test_data
window w1 as (partition by grp),
       w2 as (w1 order by val)
order by grp, val

 grp    val    s1     s2
-----+------+-----+-------
   1      8     8     15
   1      9    17     24
   2      3     3      3
   2      4     7      7