TRIGGER: Read NEW.values and OLD.values during "ON DUPLICATE KEY UPDATE"

Question

I'm trying to write a mini-auditing system for individual tables in MySQL.

I had good luck working with basic INSERT/UPDATE/DELETE commands, however now a table I'm interested in auditing uses INSERT ... ON DUPLICATE KEY UPDATE.

By using a trigger ON BEFORE INSERT I can tell this event is occurring, however I can only get half the data I'm interested in. NEW.values are readily available, but I've no idea how to get the OLD.values that came before. I suppose I could do a query using the NEW.ID in existing table, but I'm not sure about performance and reliability.

I need the OLD.values because I'm storing both old and new values for each change event since I read somewhere that was a good idea for collapsing data etc...

Is there a way in MySQL 5.0 (or newer GA release) to reliably retrieve these values as though I were in an UPDATE trigger?

EDIT: Another wrinkle:

Looks like the NEW.values do not match the data after update. They match the INSERT statement not the ON DUPLICATE KEY UPDATE data that will actually go into the record.

Answer 1

It looks like the trigger event ON AFTER UPDATE also catches the ON DUPLICATE KEY UPDATE change. From here, I was able to get OLD/NEW values and perform the logging I needed to perform.