Question

I need to change this trigger to point to the column that just got updated so what do I change NEW.song_id to?? Thanks!

DROP TRIGGER IF EXISTS `ratings_update`//
CREATE TRIGGER `ratings_update` AFTER UPDATE ON `ratings2`
FOR EACH ROW update SONGS set
rating_sum = rating_sum + NEW.rating,
rating = rating_sum / rating_count
where id = NEW.song_id
//

EDIT vvv

DROP TRIGGER IF EXISTS `ratings_upd`//
CREATE TRIGGER `ratings_upd` AFTER UPDATE ON `ratings2`
FOR EACH ROW update SONGS set
rating_sum = rating_sum + NEW.rating - OLD.rating,
rating_count = rating_count,
rating = rating_sum / rating_count
where id = NEW.song_id
//

This is what I came up with for my trigger but it is throwing me this error when I run it..

1064 – You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘// CREATE TRIGGER ratings_upd AFTER UPDATE ON ratings2 FOR EACH ROW update ‘ at line 1

Answer 1

OLD accesses values before the update, and NEW accesses values after the update.

From http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html:

You can refer to columns in the subject table (the table associated with the trigger) by using the aliases OLD and NEW. OLD.col_name refers to a column of an existing row before it is updated or deleted. NEW.col_name refers to the column of a new row to be inserted or an existing row after it is updated.