Build a SQL with sum - oracle11g

Question

Here is my table - PK is (Con_num, version, order) :
Con_num version operation amount
15 1 A 1
15 1 B 2
15 1 C 3
15 2 A 4
15 3 A 5
15 3 B 6
15 4 C 7
Con_num is the contract number.
version is the version number.
operation is just an ID for an operation.
amount is the amount of the operation.
I would like to have the total amount per version. The tricky part is that: for version 1, i just have to sum the amount. But for version 2, I need to sum the version 2 line (with operation = A) and to take the two lines from version 1 (with operation != A). Therefore, for version 3, i will take the two lines of version 3, and only the line with operation = C from version 1. Any new operation invalidate the one from the previous versions.
The result will be:
Con_num version amount
15 1 6 (1 + 2 + 3)
15 2 9 (4 + 2 + 3)
15 3 14 (5 + 6 + 3)
15 4 18 (5 + 6 + 7)
How can I do that ?

Answer 1

For each con_num and version add up all records
for the same con_num
with no version greater than the version in question
having the highest version per operation
To get the amount of the record with the highest version can be solved with Oracle's KEEP FIRST/LAST:
select
base.con_num,
base.version,
(
select sum(max(mytable.amount) keep (dense_rank last order by mytable.version))
from mytable
where mytable.con_num = base.con_num
and mytable.version <= base.version
group by mytable.con_num, mytable.operation
) as total
from (select distinct con_num, version from mytable) base;

Answer 2

select
Con_num, version, orderno, a0+a1+a2 as amount
from (
select
Con_num, version, orderno
, lag(amount,2) over(partition by Con_num order by version, orderno) a2
, lag(amount,1) over(partition by Con_num order by version, orderno) a1
, amount a0
, row_number() over(partition by Con_num, version order by orderno desc) as rn
from table1
) d
where rn = 1
You seem to want only the "most recent" combinations of (Con_num, version, orderno) which can be identified using row_number() and the values required established using lag(,1) and lag(,2) but I don't reach the stated result.
result:
| con_num | version | orderno | amount |
|---------|---------|---------|--------|
| 15 | 1 | 3 | 37 |
| 15 | 2 | 1 | 42 |
| 15 | 3 | 2 | 35 |
sqlfiddle example

Answer 3

Using LAST_VALUE analytic function.
select con_num, version, q1+q2+q3
from (
select x.*,
last_value(case when operation = 1 then amount end) ignore nulls over (order by version) q1,
last_value(case when operation = 2 then amount end) ignore nulls over (order by version) q2,
last_value(case when operation = 3 then amount end) ignore nulls over (order by version) q3
from x
)
group by con_num,version, q1, q2, q3
order by con_num,version;