Converting mysql trigger to pl/sql trigger - mysql

Question

I have created a trigger for my mysql project previously and it was working well. However, I am trying to change this trigger to make suitable for pl-sql(oracle). This is my original code which works in the mysql:
DELIMITER $$
CREATE TRIGGER course_title_delete AFTER DELETE on Course
FOR EACH ROW
BEGIN
DECLARE rownumber INT;
SET rownumber = (SELECT COUNT(*) FROM Course
WHERE Course_code=old.Course_code);
IF rownumber = 0
THEN
DELETE FROM Course_title
WHERE Course_title.Course_code=old.Course_code;
END IF;
END$$
DELIMITER ;
And this one is the same code which I have tried to convert pl-sql format. However it is not working, when I upload as a script and try to run it in apex.
CREATE OR REPLACE TRIGGER course_title_delete
AFTER DELETE ON course
FOR EACH ROW
BEGIN
DECLARE rownumber INT;
SET rownumber = (SELECT COUNT(*) FROM course
WHERE course_code= :old.course_code);
IF rownumber = 0
THEN
DELETE FROM course_title
WHERE course_title.course_code:=:old.course_code;
END IF;
END;
/

Answer 1

At the very least, you have a syntax error in this line:
DELETE FROM course_title
WHERE course_title.course_code:=:old.course_code;
----------------------------------^
That should just be =.
Also, in Oracle, the DECLARE goes before the BEGIN, not after.
Also, in Oracle, this line:
SET rownumber = (SELECT COUNT(*) FROM course
WHERE course_code= :old.course_code);
should be:
SELECT COUNT(*) INTO rownumber
FROM course
WHERE course_code = :old.course_code;
Well, actually, the is the correct syntax for what you are expressing. But, you should be using NOT EXISTS rather than COUNT(*) in both databases.
In both databases, I think you can replace this trigger with a cascading delete foreign key constraint. Also, you can simplify the logic to eliminate the if:
CREATE OR REPLACE TRIGGER course_title_delete
AFTER DELETE ON course
FOR EACH ROW
BEGIN
DELETE FROM course_title
WHERE NOT ExISTS (SELECT 1
FROM course c
WHERE c.course_code = :old.course_code
) AND
course_code = :old.course_code;
END;