Use trigger to determine to implement insert or not - sql

Question

I am a beginner of SQL and Oracle database, and I need a little help about trigger. Here is the question:
I need to create a trigger that before insert a row into table Room, it will check this new row's hotel_id to see if it exists in another table Hotel. If the new hotel_id exists, then do the insert; if not, cancel this insert.
My code:
CREATE OR REPLACE TRIGGER TRIGGER1
BEFORE INSERT ON ROOM
FOR EACH ROW
BEGIN
if (:new.hotel_id in (select hotel_id from hotel)) then
--execute the insert;
else
--cancel the insert;
end if;
END;
I'm not sure that SQL has syntax that can be used to continue or cancel an operation. If there is, please teach me or attach the link related to it.

Answer 1

Correct way of doing this is using foreign key constraints.
You can define/alter your room table to refer it in the hotel_id column.
CREATE TABLE:
create table room (
. . .,
hotel_id int not null,
constraint fk_hotel_id foreign key (hotel_id)
references hotel(hotel_id)
);
ALTER TABLE:
alter table room
add constraint fk_hotel_id foreign key (hotel_id)
references hotel(hotel_id);
If the two table exists in different databases, then you can use trigger.
You can use raise_application_error proc to abort the execution and throw error.
create or replace trigger trigger1
before insert or update
on room for each row
declare
n integer := 0;
begin
select count(*) into n
from hotel
where hotel_id = :new.hotel_id;
if n = 0 then
raise_application_error(-20001, 'Hotel ID doesn't exist');
end if;
end;

Answer 2

As GurV said, foreign keys are more appropriate way for doing this
Though, here is trigger way:
CREATE OR REPLACE TRIGGER TRIGGER1
BEFORE INSERT ON ROOM
FOR EACH ROW
declare myvar INT;
BEGIN
SELECT 1 INTO myvar FROM Hotel WHERE hotel_id = :NEW.hotel_id FETCH NEXT 1 ROW ONLY;
exception
when no_data_found then
RAISE_APPLICATION_ERROR (-20000, 'some_error_message');
END;