Can't use case & aggregation correctly - sql

Question

I have the following table
Cash_table
ID Cash Rates Amount
1 50 3 16
2 100 4 25
3 130 10 7
3 130 10 6
4 13 7 1.8
5 30 8 2.5
5 30 10 1
6 10 5 2
What I want as a result is to cumulate all the entries that have a Count(id)>1 like this:
ID New_Cash New_Rates New_Amount
1 50 3 16
2 100 4 25
3 130 10+10 130/(10+10)
4 13 7 1.8
5 30 8+10 30/(8+10)
6 10 5 2
So I only want to change the rows where Count(id)>1 and leave the rest like it was.
For the rows with count(id)>1 I want to sum up the rates and take the cash and divide it by the sum of the rates. The Rates alone aren't a problem since I can sum them up and group by id and get the desired result.
The problem is with the New_Amount column:
I am trying to do it with a case statement but it isn't working:
select id,
cash as new_cash,
sum(rates) as new_rates,
(case count(id)
when 1 then amount
else cash/sum(nvl(rates,null))
end) as new_amount
from Cash_table
group by id

Answer 1

As the cash value is always the same for an ID, you can group by that as well:
select id,
cash as new_cash,
sum(rates) as new_rates,
case count(id)
when 1 then max(amount)
else cash/sum(rates)
end as new_amount
from cash_table
group by id, cash
order by id
ID NEW_CASH NEW_RATES NEW_AMOUNT
---------- ---------- ---------- ----------
1 50 3 16
2 100 4 25
3 130 20 6.5
4 13 7 1.8
5 30 18 1.66666667
6 10 5 2
The first branch of the case expression needs an aggregate because you aren't grouping by amount; and the sum(nvl(rates,null)) can just be sum(rates). If you're expecting any null rates then you need to decide how you want the amount to be handled, but nvl(rates,null) isn't doing anything.
You can do the same thing without a case expression if you prefer, manipulating all the values - which might be more expensive:
select id,
cash as new_cash,
sum(rates) as new_rates,
sum(amount * rates)/sum(rates) as new_amount
from cash_table
group by id, cash
order by id