Create a trigger after insert with a select in mysql - mysql

Question

I am trying to create a mysql trigger. The error code 1064 is very generic. The trigger is to see if a record exists for a particular key; and if it does update a particular column in the newly inserted row with that value. I am using a select query on the same table as the trigger is on. Does that cause a problem? Here is the code:
DELIMITER $$
CREATE TRIGGER classid_insert
AFTER INSERT ON courses_semester
FOR EACH ROW
BEGIN
SET #class_id = (SELECT class_id FROM courses_semester WHERE
course_id = NEW.`course_id`
AND `dept_id` = NEW.`dept_id`
AND `univ_id` = NEW.`univ_id`
AND `section_id` = NEW.`section_id`
AND `semester` = NEW.`semester`
AND `year` = NEW.`year`);
IF(#class_id = NULL)
THEN
NEW.class_id = UUID()
ELSE
NEW.class_id = #class_id
END IF;
END
DELIMITER ;

Answer 1

your entire trigger code should look like below. remove the spaces after DELIMITER $$ and before DELIMITER ;. Also, the last END need to changed to END $$. Also, it has to be an BEFORE trigger and not an AFTER trigger.
Moreover, NEW.class_id = UUID() is not correct.It's missing SET as
SET NEW.class_id = UUID();
CORRECTED TRIGGER CODE:
DELIMITER $$
CREATE TRIGGER classid_insert
BEFORE INSERT ON courses_semester
FOR EACH ROW
BEGIN
SET #class_id = (SELECT class_id FROM courses_semester WHERE
course_id = NEW.`course_id`
AND `dept_id` = NEW.`dept_id`
AND `univ_id` = NEW.`univ_id`
AND `section_id` = NEW.`section_id`
AND `semester` = NEW.`semester`
AND `year` = NEW.`year`);
IF(#class_id = NULL)
THEN
SET NEW.class_id = UUID();
ELSE
SET NEW.class_id = #class_id;
END IF;
END $$
DELIMITER ;