Reduce the value of a vehicle every month - sql

Question

What I am trying to do is to reduce the value of every vehicle in the 'Vehicle' table so that when the date reaches one month past the 'LastUpdate' value the 'Value' column is reduced by 2.5%. The trigger should run AFTER LOGON ON DATABASE. The problem is, a DBA may not logon to the database every day, so if it is has been six months since the last logon, the trigger will loop through, reduce the value by 2.5% and do ADD_MONTHS(LastUpdate, 1).
My code for the function that will calculate the value is:
REATE OR REPLACE FUNCTION fn_Vehicle_Value
(VehicleNumber IN NUMBER,
VehicleValue IN OUT NUMBER)
RETURN NUMERIC
IS
BEGIN
VehicleValue := VehicleValue - (VehicleValue * 0.025);
RETURN VehicleValue;
END;
/
This is my attempt at creating the system trigger:
CREATE OR REPLACE TRIGGER tg_VehicleDepreciate
AFTER LOGON ON DATABASE
IS
CURSOR vehicle_cur IS SELECT "VALUE", LastUpdate FROM Vehicle;
BEGIN
FOR vehicle_rec IN vehicle_cur LOOP
WHILE LastUpdate < SYSDATE LOOP
LastUpdate."Value" := fn_Vehicle_Update("VALUE");
UPDATE Vehicle
SET LastUpdate := ADD_MONTHS(LastUpdate, 1)
WHERE Vehicle# = vehicle_cur.Vehicle#;
END LOOP;
EXIT WHEN vehicle_cur%NOTFOUND;
END LOOP
END;
/
From what I can tell, my function is right. But the trigger does not compile and produces the following error report:
Error report -
ORA-04079: invalid trigger specification
04079. 00000 - "invalid trigger specification"
*Cause: The create TRIGGER statement is invalid.
*Action: Check the statement for correct syntax.
I am guessing it is a syntax error, but there may also be a logical error that I cannot work out.

Answer 1

SHOW ERRORS after compiling your trigger would reveal all errors.
Here are few..
1) in update, it is just SET somecolumn = Somevalue
2) oracle implicitly opens the cursor and closes to, when used with a FOR loop.
3) after using FOR loop,the fetched results should be used like.. Forloopvariable.column-name
4) added Vehicle# to your cursor.
5) added V_date logic.
CREATE OR REPLACE TRIGGER tg_VehicleDepreciate
AFTER LOGON ON DATABASE
IS
CURSOR vehicle_cur IS SELECT "VALUE", LastUpdate ,Vehicle# FROM Vehicle;
V_date DATE;
BEGIN
FOR vehicle_rec IN vehicle_cur LOOP
V_date := vehicle_rec.LastUpdate;
WHILE V_date < SYSDATE LOOP
/* what are you trying here? */
---vehicle_rec."Value" := fn_Vehicle_Update("VALUE");
UPDATE Vehicle
SET LastUpdate = ADD_MONTHS(LastUpdate, 1)
WHERE Vehicle# = vehicle_rec.Vehicle#;
V_date := ADD_MONTHS( V_date,1);
END LOOP;
END LOOP
END;
/