How to fix the trigger with check compiler log error? - sql

Question

Please, help!
I have trigger:
CREATE TRIGGER check_reservation BEFORE INSERT ON order
FOR EACH ROW
DECLARE mistake INTEGER;
BEGIN
SELECT count(*) INTO mistake FROM order join reserving
on id_order = reserving.order_id_order
WHERE reserving.room_num_room=:new.room_num_room
AND (order.reservation_from < :new.reservation_from AND :new.reservation_from < order.reservation_to) OR
(order.reservation_from < :new.reservation_from AND :new.reservation_to < order.reservation_to) OR
(:new.reservation_from <= order.reservation_from AND order.reservation_to <= :new.reservation_to);
IF mistake>0 THEN
raise_application_error(-20001,'reservation already exists');
END IF;
END;
The idea of the trigger is not to allow make a reservation on already booked room. When I run it I had check compiler log error message. How can I change trigger?
I have following tables:
CREATE TABLE order (
id_order CHAR(100) NOT NULL,
reservation_from DATE NOT NULL,
reservation_to DATE NOT NULL,
);
ALTER TABLE order ADD CONSTRAINT order_pk PRIMARY KEY ( id_order );
CREATE TABLE room (
num_room CHAR(100) NOT NULL,
type VARCHAR2(100) NOT NULL,
);
ALTER TABLE room ADD CONSTRAINT room_pk PRIMARY KEY ( num_room );
CREATE TABLE reserving (
room_num_room CHAR(100) NOT NULL,
order_id_order CHAR(100) NOT NULL
);
ALTER TABLE reserving ADD CONSTRAINT reserving_pk PRIMARY KEY ( room_num_room,
order_id_order );
ALTER TABLE reserving
ADD CONSTRAINT reserving_order_fk FOREIGN KEY ( order_id_order )
REFERENCES order ( id_order );
ALTER TABLE reserving
ADD CONSTRAINT reserving_room_fk FOREIGN KEY ( room_num_room )
REFERENCES room ( num_room );

Answer 1

I tried recreating the trigger with the statements above. The statements failed with several errors, it looks as if they were not tested before posting them as question. Please take some time posting a quality question.
Example:
CREATE TABLE room (
num_room CHAR(100) NOT NULL,
type VARCHAR2(100) NOT NULL, << this trailing comma makes this statement fail.
);
After fixing all errors I ran the "CREATE TRIGGER" and it errored out with
PLS-00049: bad bind variable 'NEW.ROOM_NUM_ROOM'
That is because the column ROOM_NUM_ROOM does not exist in the "ORDER" table.
If I remove the reference to 'NEW.ROOM_NUM_ROOM' the trigger compiles successfully.
However, as gsalem pointed out, this will not work because it will raise a mutating table error. In the trigger code you cannot execute DML referencing the table that the trigger is on. There is plenty of documentation on how to avoid mutating table errors.