Приблизительно так

create table #table1 (id int identity, inv_period char(7), summa decimal(10,2))

insert into #table1 values('2001/01', 10)
insert into #table1 values('2001/02', 15)
insert into #table1 values('2001/03', 7)
insert into #table1 values('2001/04', 20)
insert into #table1 values('2001/05', 10)

select a.inv_period, max(a.summa) as summa1, sum(coalesce(b.summa, 0)) as summa2
from #table1 a
left outer join #table1 b on b.inv_period < a.inv_period
group by a.inv_period

drop table #table1