TRIGGER does not fire for deleting, but fire for inserting and updating - plsql

Question

This is my first time creating Trigger. I found some similar questions, but I still cannot solve my error from those suggestions so I will ask here. Here are my tables:
Create Table Bill
(
Bill_Number Number(6,0) primary key,
Paid_YN Char(1),
Posted_YN Char(1)
);
And this table:
Create Table Bill_Item
(
Bill_Number Number(6,0) References Bill (Bill_Number),
Menu_Item_Number Number(5,0),
Quantity_Sold Number(3,0),
Selling_Price Number(6,2)
);
I need to create a trigger to prevent any insert, update, or delete on Bill_Item table if Paid_YN or/and Posted_YN is 'Y'. The messages must show which event and what reason (paid, posted or both).
And this is my code. Trigger works well with inserting, and updating but does not fire with deleting.
CREATE OR REPLACE TRIGGER TR_NO_POST
BEFORE INSERT OR UPDATE OR DELETE ON Bill_Item
FOR EACH ROW
BEGIN
SELECT Paid_YN, Posted_YN
INTO V_Paid_YN, V_Posted_YN
FROM Bill
WHERE Bill_Number = :NEW.Bill_Number;
IF inserting THEN
IF V_Paid_YN = 'Y' AND V_Posted_YN = 'N' THEN
RAISE_APPLICATION_ERROR(-20001, 'Bill has been paid. Cannot add more items!');
ELSIF V_Posted_YN = 'Y' AND V_Paid_YN = 'N'THEN
RAISE_APPLICATION_ERROR(-20002, 'Bill has been posted. Cannot add more items!');
ELSIF V_Paid_YN = 'Y' AND V_Posted_YN = 'Y' THEN
RAISE_APPLICATION_ERROR(-20003, 'Bill has been paid and posted. Cannot add more items!');
END IF;
ELSIF updating THEN
IF V_Paid_YN = 'Y' AND V_Posted_YN = 'N' THEN
RAISE_APPLICATION_ERROR(-20011, 'Bill has been paid. Cannot change!');
ELSIF V_Posted_YN = 'Y' AND V_Paid_YN = 'N'THEN
RAISE_APPLICATION_ERROR(-20022, 'Bill has been posted. Cannot change!');
ELSIF V_Paid_YN = 'Y' AND V_Posted_YN = 'Y' THEN
RAISE_APPLICATION_ERROR(-20033, 'Bill has been paid and posted. Cannot change!');
END IF;
ELSIF deleting THEN
IF V_Paid_YN = 'Y' AND V_Posted_YN = 'N' THEN
RAISE_APPLICATION_ERROR(-20111, 'Bill has been paid. Cannot delete!');
ELSIF V_Posted_YN = 'Y' AND V_Paid_YN = 'N'THEN
RAISE_APPLICATION_ERROR(-20222, 'Bill has been posted. Cannot delete!');
ELSIF V_Paid_YN = 'Y' AND V_Posted_YN = 'Y' THEN
RAISE_APPLICATION_ERROR(-20333, 'Bill has been paid and posted. Cannot delete!');
END IF;
END IF;
END TR_NO_POST;

Answer 1

You have to select from "Bill table" to check Paid_YN column value.
Something like this:
CREATE OR REPLACE TRIGGER TR_NO_POST
BEFORE INSERT OR UPDATE OR DELETE ON Bill_Item
FOR EACH ROW
paid_res Char(1);
posted_res Char(1);
BEGIN
select max(h.paid_yn),
max(h.posted_yn)
into paid_res, posted_res
from Bill h
where h.Bill_Number = :NEW.Bill_Number;
if paid_res = 'Y' then
RAISE_APPLICATION_ERROR(-20001, 'Bill has been paid!');
elsif posted_res = 'Y' then
RAISE_APPLICATION_ERROR(-20001, 'Bill has been posted!');
end if;
END TR_NO_POST;