PL/SQL ORACLE: Trigger updates on delete - sql

Question

I am trying to make a trigger that increases the booked value and decreases the available value whenever new record is inserted inside the table ticket_price. If a record is deleted, I want it to decrease the booked value and increase the available value.
Although I am able to successfully make the trigger work for INSERT, I am unable to do the same for updating the values on deletion of a record.T his is the error I get whenever I try to delete a record
ORA-01403: no data found
ORA-06512: at "K.CAL", line 6
ORA-04088: error during execution of trigger 'K.CAL'
Just to clarify, I am updating values in another table, not the same table I am deleting!
Here is my code for the trigger:
CREATE OR REPLACE TRIGGER cal
BEFORE INSERT OR DELETE ON TICKET_PRICE FOR EACH ROW
DECLARE
V_TICKET TICKET_PRICE.TICKETPRICE%TYPE;
V_BOOKED FLIGHTSEAT.BOOKED_SEATS%TYPE;
V_AVAILABLE FLIGHTSEAT.AVAILABLE_SEATS%TYPE;
BEGIN
SELECT BOOKED_SEATS,AVAILABLE_SEATS
INTO V_BOOKED,V_AVAILABLE
FROM FLIGHTSEAT
WHERE SEAT_ID=:NEW.SEAT_ID;
IF INSERTING THEN
V_BOOKED:=V_BOOKED+1;
V_AVAILABLE:=V_AVAILABLE-1;
UPDATE FLIGHTSEAT
SET BOOKED_SEATS=V_BOOKED, AVAILABLE_SEATS=V_AVAILABLE
WHERE SEAT_ID=:NEW.SEAT_ID;
ELSIF DELETING THEN
V_BOOKED:=V_BOOKED-1;
V_AVAILABLE:=V_AVAILABLE+1;
UPDATE FLIGHTSEAT
SET BOOKED_SEATS=V_BOOKED, AVAILABLE_SEATS=V_AVAILABLE
WHERE SEAT_ID=1;
END IF;
END;

Answer 1

You have correctly surmised that :new.seat is not available on the update for a delete. But neither is it available for the select and ow could you know sea_id=1 was need to be updated? For reference to Deleted row data use :Old.column name; is this case use :old_seat_id for both select and update.
But you don't need the select at all. Note: Further you have an implied assumption that seat_id is unique. I'll accept that below.
create or replace trigger cal
before insert or delete on ticket_price
for each row
declare
v_seat_id flightseat.seat_id%type;
v_booked flightseat.booked_seats%type;
begin
if INSERTING then
v_booked := 1;
v_seat_id := :new.seat_id;
else
v_booked := -1;
v_seat_id := :old.seat_id;
end if;
update flightseat
set booked_seats=booked_seats+v_booked
, available_seats=available_seats-v_booked
where seat_id = v_seat_id;
end;