Dynamic column value to be set as next row's another column value in Oracle [closed] - oracle

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I am new to Oracle and I would like to form an Oracle query:
Id CrLmt Type Unit Price Amount Prev_bal NewBal
5-00001 100000 Sell 100 150 15000 100000 85000
Buy 75 600 45000 85000 130000
Buy 85 550 46750 130000 176750
Sell 60 1000 60000 176750 116750
5-00002 90000 Sell 100 400 40000 90000 50000
Buy 550 300 165000 50000 215000
Sell 300 1000 300000 215000 -85000
My conditions are as follows:
ID and CrLmt are combination and its subsequent rows come under this ID, CrLmt combination.
For every ID, CrLmt combination, the CrLmt will be assigned in Prev_Bal column, rest of the rows will have a calculation
Based on Buy/Sell in Type column, the values in Amount and Prev_Bal will be added or subtracted and the resultant value should be displayed in NewBal (dynamic) column
If the Type is "Sell" then the value in PrevBal should be subtracted with Amount column value and if the Type is "Buy" then then the value in PrevBal should be added with Amount column value and the resultant value should be displayed in NewBal (dynamic) column in the corresponding row
The value obtained in NewBal column in row 1 should be displayed in row 2 Prev_Bal column for 2nd row's calculation and so on.
If any negative value occurs in NewBal column the same needs to be carried out to next calculations.
I tried using LAG function to get previous values but doesn't know how to get a dynamic column's (NewBal) values on the go.

Answer 1

Here is a little example that you will have to adapt to your current structure. You will need a date on your transaction for the order clause of the sum.
all you need is a running sum to which you will either add the credit limit for the new_balance or to which you will take the previous row for the old_balance
--TEST DATA
CREATE TABLE credit_limit ( id varchar2(10), crlmt number );
CREATE TABLE transactions (transaction_type varchar2(4), unit number, price number, amount number, crlmt_id varchar2(10), date_transaction date );
INSERT INTO credit_limit values ('5-00001',100000);
INSERT INTO credit_limit values ('5-00002',90000);
INSERT INTO transactions values ('Sell',100,150,15000,'5-00001',sysdate-4);
INSERT INTO transactions values ('Buy',75,600,45000,'5-00001',sysdate-3);
INSERT INTO transactions values ('Buy',85,550,46750,'5-00001',sysdate-2);
INSERT INTO transactions values ('Sell',60,1000,60000,'5-00001',sysdate-1);
INSERT INTO transactions values ('Sell',100,400,40000,'5-00002',sysdate-3);
INSERT INTO transactions values ('Buy',550,300,165000,'5-00002',sysdate-2);
INSERT INTO transactions values ('Sell',300,1000,300000,'5-00002',sysdate-1);
--The query
select cr.id, cr.crlmt, tr.transaction_type, tr.unit, tr.price, tr.amount,
NVL(cr.crlmt + SUM(tr.amount*decode(tr.transaction_type,'Sell',-1,'Buy',1))
OVER (partition by cr.id order by cr.id, tr.date_transaction
rows between unbounded preceding and 1 preceding ),Cr.crlmt) old_bal,
cr.crlmt + SUM(tr.amount*decode(tr.transaction_type,'Sell',-1,'Buy',1))
OVER (partition by cr.id order by cr.id, tr.date_transaction
rows between unbounded preceding and current row ) new_bal
from
credit_limit cr
JOIN
transactions tr
ON cr.id=tr.crlmt_id
order by cr.id, tr.date_transaction
result :
ID CRLMT TRAN UNI PRICE AMOUNT OLD_BAL NEW_BAL
5-00001 100000 Sell 100 150 15000 100000 85000
5-00001 100000 Buy 75 600 45000 85000 130000
5-00001 100000 Buy 85 550 46750 130000 176750
5-00001 100000 Sell 60 1000 60000 176750 116750
5-00002 90000 Sell 100 400 40000 90000 50000
5-00002 90000 Buy 550 300 165000 50000 215000
5-00002 90000 Sell 300 1000 300000 215000 -85000