with t as (
	select 'a' a, 10 b from dual union all
	select 'b' a, 2  b from dual union all
	select 'b' a, 10 b from dual union all
	select 'c' a, 2  b from dual union all
	select 'c' a, 3  b from dual union all
	select 'c' a, 10 b from dual
)

a	10
b	20
c	60

with t as (
	select 'a' a, 10 b from dual union all
	select 'b' a, 2  b from dual union all
	select 'b' a, 10 b from dual union all
	select 'c' a, 2  b from dual union all
	select 'c' a, 3  b from dual union all
	select 'c' a, 10 b from dual
), t1 as (
	select 
		a,
		b b0,
		nvl(lag(b) over (partition by a order by b),1) b1,
		nvl(lag(b,2) over (partition by a order by b),1) b2,
		nvl(lag(b,3) over (partition by a order by b),1) b3,
		nvl(lag(b,4) over (partition by a order by b),1) b4,
		nvl(lag(b,5) over (partition by a order by b),1) b5,
		nvl(lag(b,6) over (partition by a order by b),1) b6
	from t
)
select
	a, max(b0*b1*b2*b3*b4*b5*b6) b
from t1
group by a