Calculate current based on previous formula - oracle

Question

I have a scenario where the current column value is calculated based on the previous value calculated by the formula
The initial row of the group has no previous value so it will not consider.
Formula for loss= relase-withdraw-least(previous_row_loss,reverse)
Here below loss is the column I need to calculate.
I tried with the following query but not getting expected output. Can you please guide me here.
SELECT
pid,release,withdraw,reverse,
SUM(release - withdraw - LEAST( LAG(loss,1,0) OVER (ORDER BY pid)),reverse)) as loss
FROM transactions

Answer 1

You can use a MODEL clause:
SELECT *
FROM (
SELECT t.*,
ROW_NUMBER() OVER (ORDER BY pid, fiscalperiod) AS rn
FROM table_name t
)
MODEL
DIMENSION BY (rn)
MEASURES (pid, fiscalperiod, release, withdraw, reverse, 0 AS loss)
RULES (
loss[1] = release[1] - withdraw[1] - reverse[1],
loss[rn>1] = release[cv()] - withdraw[cv()] - LEAST(reverse[cv()], loss[cv()-1])
+ loss[cv()-1]
);
Or, probably, much less efficiently a recursive query:
WITH numbered_rows AS (
SELECT t.*,
ROW_NUMBER() OVER (ORDER BY pid, fiscalperiod) AS rn
FROM table_name t
),
recursive_query (rn, pid, fiscalperiod, release, withdraw, reverse, loss) AS (
SELECT rn,
pid,
fiscalperiod,
release,
withdraw,
reverse,
release - withdraw - reverse
FROM numbered_rows
WHERE rn = 1
UNION ALL
SELECT n.rn,
n.pid,
n.fiscalperiod,
n.release,
n.withdraw,
n.reverse,
n.release - n.withdraw + GREATEST(r.loss - n.reverse, 0)
FROM numbered_rows n
INNER JOIN recursive_query r
ON (n.rn = r.rn + 1)
)
SELECT *
FROM recursive_query;
Which, for your sample data:
CREATE TABLE table_name (pid, fiscalperiod, release, withdraw, reverse) AS
SELECT 'A1', 2022001, 10, 10, 10 FROM DUAL UNION ALL
SELECT 'A1', 2022002, 20, 13, 2 FROM DUAL UNION ALL
SELECT 'A1', 2022003, 20, 20, 10 FROM DUAL UNION ALL
SELECT 'A2', 2022002, 15, 10, 13 FROM DUAL;
Both output:
RN
PID
FISCALPERIOD
RELEASE
WITHDRAW
REVERSE
LOSS
1
A1
2022001
10
10
10
-10
2
A1
2022002
20
13
2
7
3
A1
2022003
20
20
10
0
4
A2
2022002
15
10
13
5
db<>fiddle here