Issue using an INSTEAD OF trigger

Question

Hi Guys,
I've not posted in here before so please tell me if i'm asking too much or just not doing something right.
I have created the following view which will compile ok:
DROP VIEW book_cust_vu;
CREATE VIEW book_cust_vu AS
SELECT c.cust_id, c.name, c.tel_no, b.table_no, b.book_date, b.time, b.book_id, b.notes, b.rest_id
FROM booking b, customer c
WHERE c.cust_id = b.cust_id;
I am trying to create and INSTEAD OF trigger that will not allow an update to occur that matches and existing combination of b.table_no, b.rest_id and b.book_date. I have come up with the following:
CREATE OR REPLACE TRIGGER book_chk
INSTEAD OF UPDATE ON book_cust_vu
FOR EACH ROW
DECLARE
tableno               book_cust_vu.table_no%TYPE;
bookdate          book_cust_vu.book_date%TYPE;
restid               book_cust_vu.rest_id%TYPE;     
BEGIN
SELECT table_no, book_date, rest_id
INTO tableno, bookdate, restid
FROM book_cust_vu
WHERE book_id = :new.book_id;
DBMS_OUTPUT.PUT_LINE('rest_id = '||restid);
DBMS_OUTPUT.PUT_LINE('table_no = '||tableno);
DBMS_OUTPUT.PUT_LINE('book_date = '||bookdate);
IF :new .table_no != tableno AND
:new.book_date != bookdate AND
:new.rest_id != restid THEN
UPDATE booking
SET table_no = :new.table_no,
book_date = :new.book_date,
time = :new.time,
notes = :new.notes,
rest_id = :new.rest_id,
book_id = :new.book_id
WHERE book_id = :new.book_id;
ELSE
DBMS_OUTPUT.PUT_LINE('This booking matches an existing one');
END IF;
END;
The DBMS outputs confirm that the variables are being populated with values that math existing combinations of those records, but the statement:
IF :new .table_no != tableno AND
:new.book_date != bookdate AND
:new.rest_id != restid THEN
does not seem to find this combination. The last DBMS output will also print, so that seems to confirm that the above statement is working in part, as DBMS output should only appear if the first IF statement is false. So basically, it will allow duplicates of the table_no, book_date, rest_id combo.
This is my test update line:
UPDATE book_cust_vu SET table_no = '1', rest_id = '1', book_date = '30-OCT-05' WHERE book_id = 3;
The combination of values for table_no, book_date, rest_id already exist for another record.
I have run out of ideas and simply comparing :new.variable != :old.variable will also allow the update to occur.
If anyone can spot what is wrong or anything I need to change, that would be really helpful!!!
Thanks,
Anton

Answer 1

Hi,
Thanks for the suggestions guys, managed to get it going with a cursor instead:
CREATE OR REPLACE TRIGGER book_chk
INSTEAD OF UPDATE ON book_cust_vu
FOR EACH ROW
DECLARE
temp          NUMBER;
CURSOR book_count IS
SELECT count(*)
INTO temp
FROM book_cust_vu
WHERE book_date = :new.book_date
AND table_no = :new.table_no
AND rest_id = :new.rest_id;
BEGIN
OPEN book_count;
LOOP
FETCH book_count INTO temp;
EXIT WHEN book_count%NOTFOUND;
IF(temp = 1) THEN
RAISE_APPLICATION_ERROR(-20012,
     'This booking matches an existing one');
ELSE
UPDATE booking
SET table_no = :new.table_no,
book_date = :new.book_date,
time = :new.time,
notes = :new.notes,
rest_id = :new.rest_id,
book_id = :new.book_id
WHERE book_id = :new.book_id;
END IF;
END LOOP;
CLOSE book_count;
END;
Worked on the first test, but we'll see!