Updating Column - oracle

Question

I created a table with the following attributes :
TABLE "VENDORACCOUNT"
( "VEN_ACCOUNTID"
"VEN_REGNO"
"VEN_TXDATE"
"VEN_INVOICE_REFNO"
"TOTALAMOUNT"
"PAID_TOVEN"
"BALANCE"
)
I take the TOTALAMOUNT column value through a POPUP LOV from another table on the basis of its VEN_INVOICE_REFNO value. Here the scenario is that the TOTALAMOUNT column value is subtracted from the PAID_TOVEN column value. But the next time I select the TOTALAMOUNT value it does not show me the updated value. It shows me the old value as shown in the report below.
Query of Report:
select "VEN_ACCOUNTID",
"VEN_REGNO" ,
"VEN_TXDATE" ,
"VEN_INVOICE_REFNO" as ,
"TOTALAMOUNT" as ,
"PAID_TOVEN" as ,
TOTALAMOUNT-PAID_TOVEN as "Balance"
from "VENDORACCOUNT"
In the above report I want that whenever I do the second entry it should show me the subtracted or updated value ie 1800 instead of 2800 and 4550 instead of 9550 respectively. So the next time I can subtract the amount from 1800 and 4550.
I created this trigger
create or replace trigger "VENDORACCOUNT_T2"
BEFORE
insert or update or delete on "VENDORACCOUNT"
for each row
begin
DECLARE new_balance INT;
DECLARE new_total INT;
DECLARE new_paid INT;
SELECT balance INTO old_balance,
total INTO old_total,
PAID_TOVEN INTO new_paid
FROM vendoraccount
WHERE ven_regno = new.ven_regno
AND VEN_INVOICE_REFNO = new.VEN_INVOICE_REFNO;
UPDATE vendoraccount SET TOTALAMOUNT = old_total + old_balance - new_paid,
balance = TOTALAMOUNT - new_paid
WHERE VEN_REGNO= new.VEN_REGNO
AND VEN_INVOICE_REFNO = new.VEN_INVOICE_REFNO;
end;
and am getting this error:
ERROR: PLS-00103: 'Encountered the symbol "DECLARE" when expecting one
of the following: begin function pragma procedure subtype type current curs'

Answer 1

I think you don't need a trigger. You can create a view based on the below query and then create the RECORD GROUP for your LOV based on the VIEW. The query would look like-
select accid,regno,inv_refno,LAG(bal,1,totalamount) OVER (PARTITION BY regno ORDER BY accid) "TOTALAMOUNT", paid_toven, bal
from (with temp_data as
(select 2 accid,3 regno, 16 inv_refno, 2800 totalamount, 1000 paid_toven from dual
union
select 3 accid,3 regno, 16 inv_refno, 2800 totalamount, 2000 paid_toven from dual
union
select 4 accid,8 regno, 22 inv_refno, 9550 totalamount, 5000 paid_toven from dual
union
select 5 accid,8 regno, 22 inv_refno, 9550 totalamount, 5000 paid_toven from dual
union
select 6 accid,8 regno, 22 inv_refno, 9550 totalamount, 8000 paid_toven from dual)
select accid,regno,inv_refno,totalamount,paid_toven,totalamount-paid_toven bal
from temp_data);
The output is -
ACCID REGNO INV_REFNO TOTALAMOUNT PAID_TOVEN BAL
----- ----- --------- ----------- ---------- ---
2 3 16 2800 1000 1800
3 3 16 1800 2000 800
4 8 22 9550 5000 4550
5 8 22 4550 5000 4550
6 8 22 4550 8000 1550
So based on your table the query would be-
select accid,regno,inv_refno,LAG(bal,1,totalamount) OVER (PARTITION BY regno ORDER BY accid) "TOTALAMOUNT", paid_toven, bal
from (select accid,regno,inv_refno,totalamount,paid_toven,totalamount-paid_toven bal
from VENDORACCOUNT);
The query does pretty much what you want, but your sample data does not look right. This is actually one example of a running total.