Group by and divide

Question

I have the table below on sql of accounting accounts (A is a cost account and B a headcount ), and cc as cost center. So what i want to do is divide the amount of account A over account B for each cc

Account	cc	Amount
A	x	1
A	y	2
B	z	4
B	y	1
A	z	1
B	x	2

So the result would be:

Account	cc	Amount
A	x	1 /2
A	y	2
B	z	0
B	y	0
A	z	1 /4
B	x	0

I was thinking about a group by but Im a very beginner in sql and don't know how to use it thanks in advance for your help!

Answer 1

For the results you specify, you can use window functions:

select t.*,
       (case when account = 'A'
             then amount * 1.0 / sum(case when account = 'B' then amount end) over (partition by cc)
             else 0
        end) as ratio
from t;

Answer 2

I would just use a regular group by with some cases:

with cc_amts as (
select cc,
    sum(case when account = 'A' then amount else 0 end) amt_a,
    sum(case when account = 'B' then amount else 0 end) amt_b
from t
group by cc)
select cc, amt_a / amt_b
from cc_amts;