Progressive LOOP Statement ORACLE - oracle

Question

How to create a function that returns a float(ChargeTotal)?
ChargeTotal is based on a progressive table using number of batches.
num of batches | charge
----------------------------
1-10 | 0
11-20 | 50
21-30 | 60
31-40 | 70
40+ | 80
If number of batches is 25 then
num of batches | charge
----------------------------
1-10 | 0
11-20 | 50*10
21-30 | 60*5
----------------------------
total | 800 <number I need to be returned(ChargeTotal)
So far I have come up with the following, but I'm unsure how to get the total for each loop, or if it is even possible to do more than one FOR statements:
CREATE OR REPLACE FUNCTION ChargeTotal
RETURN FLOAT IS
total FLOAT;
BEGIN
FOR a in 1 .. 10 LOOP
FOR a in 11 .. 20 LOOP
FOR a in 21 .. 30 LOOP
FOR a in 40 .. 1000 LOOP
RETURN Total;
END ChargeTotal;

Answer 1

Ok so take into consideration that right now I have no DB available to test this (there might be some syntax errors etc).
But I am thinking something along this lines of code...
function ChargeTotal(xin number) return number is
cursor mycursor is
select lowLimit,highLimit,charge
from progressive_table order by lowLimit;
sum number;
segment number;
x number;
begin
sum:=0;
x :=xin;
for i in mycursor loop
segment := (i.highLimit-i.lowLimit)+1;
x := greatest ( x - segment,x);
sum := sum + segment*i.charge;
if (x<segment) then
return sum;
end if;
end loop;
return sum;
end;

Answer 2

I think you can do the calculation via single sql without complex function
the logic is:
you have weights for each "band"
calculate the "band" each row
count(*) over to calculate number of rows in each "band"
join your weight table to get sub.total for each band
use rollup to get grand total
sql
select r.num_of_batches
,sum(r.subtotal_charge)
from (
with weights as
(select 1 as num_of_batches, 0 as charge from dual
union all
select 2 as num_of_batches, 50 as charge from dual
union all
select 3 as num_of_batches, 60 as charge from dual
union all
select 4 as num_of_batches, 70 as charge from dual
union all
select 5 as num_of_batches, 80 as charge from dual
)
select distinct n.num_of_batches
, w.charge
, count(*) over (partition by n.num_of_batches) as cnt
, count(*) over (partition by n.num_of_batches) * charge as subtotal_charge
from (
select num, case when floor(num / 10) > 4 then 5 else floor(num / 10)+1 end as num_of_batches
from tst_brances b
) n
inner join weights w on n.num_of_batches = w.num_of_batches
order by num_of_batches
) r
group by ROLLUP(r.num_of_batches)
populate test data
create table tst_branches(num int);
declare
i int;
begin
delete from tst_brances;
for i in 1..10 loop
insert into tst_brances(num) values (i);
end loop;
for i in 11..20 loop
insert into tst_brances(num) values (i);
end loop;
for i in 21..25 loop
insert into tst_brances(num) values (i);
end loop;
for i in 31..32 loop
insert into tst_brances(num) values (i);
end loop;
for i in 41..43 loop
insert into tst_brances(num) values (i);
end loop;
for i in 51..55 loop
insert into tst_brances(num) values (i);
end loop;
commit;
end;
results
1 1 0
2 2 500
3 3 360
4 4 140
5 5 640
6 1640