SQL: Column Sum - sql

Question

Lets have following sample table:
Person Quantity
A 1
B 2
C 3
D 4
E 5
Result should be:
PersonAggregate
1 (0+Quantity of PersonA)=sumA
3 (sumA+Quantity of PersonB)=sumB
6 (sumB+Quantity of PersonC)=sumC
10 (sumC+Quantity of PersonD)=sumD
15 (sumD+Quantity of PersonE)
Is it possible to get this result in onq SQL-query?

Answer 1

Most versions of SQL support cumulative sums as a window function:
select person, sum(quantity) over (order by person) as cumesum
from sample;
You can can also do this with a correlated subquery:
select s.person,
(select sum(s2.quantity)
from samples s2
where s2.person <= s.person
) as cumesum
from sample s;

Answer 2

this will obviously get the individual sums.
select person, sum(quantity)
from sample
group by person
order by person
i don't think your desired effect can be done in a set based way. a procedural language with cursor, like T-SQL or PLSQL, can do it easily.
i'd write a stored procedure and call it.

Answer 3

If the sample table has more than one row per person with multiple quantities that need to be summed you could use:
select curr.person, curr.sum_person + case when prev.person <> curr.person
then prev.sum_person
else 0 end as person_sum
from (select person, sum(quantity) as sum_person
from sample
group by person) curr
cross join (select person, sum(quantity) as sum_person
from sample
group by person) prev
where prev.person =
(select max(x.person) from sample x where x.person < curr.person)
or curr.person = (select min(person) from sample)
group by curr.person
Fiddle: http://sqlfiddle.com/#!2/7c3135/6/0
Output:
| PERSON | PERSON_SUM |
|--------|------------|
| A | 1 |
| B | 3 |
| C | 5 |
| D | 7 |
| E | 9 |
If there is only one row per person on the sample table, you could more simply use:
select curr.person, curr.quantity + case when prev.person <> curr.person
then prev.quantity
else 0 end as person_sum
from sample curr
cross join sample prev
where prev.person =
(select max(x.person) from sample x where x.person < curr.person)
or curr.person = (select min(person) from sample)
group by curr.person
Fiddle: http://sqlfiddle.com/#!2/7c3135/8/0
Output returned is the same, because in your example, there is only one row per person.
If using Oracle, SQL Server, or a database that supports analytic functions, you could use:
If sample has one row per person:
select person,
sum(quantity) over(order by person rows between 1 preceding and current row) as your_sum
from sample
order by person
Fiddle: http://sqlfiddle.com/#!4/82e6f/1/0
If sample has 2+ rows per person:
select person,
sum(sum_person) over(order by person rows between 1 preceding and current row) as your_sum
from (select person, sum(quantity) as sum_person
from sample
group by person) x
order by person
Fiddle: http://sqlfiddle.com/#!4/82e6f/4/0