Question

I’m writing a trigger that will do a cross table update, but I can’t get the desired result. I’m working with one param, and that is messageId. Using that messageId, I need to go into the messages table and find the userId @messageId, then update his/her score: (@messageId is coming from an insert into a third table, so really it’s NEW.messageId)

      UPDATE users
      SET users.score = users.score + 1
      WHERE users.id = messages.userId

I need to select messages.userId @messageId from messages, but the trigger will not let me do a select statement, so I’m a bit stuck!

I tried this, which does not seem to work either:

      UPDATE users, messages
      INNER JOIN messages ON messages.id = NEW.messageId
      SET users.score = users.score + 1
      WHERE users.id = messages.userId

PS: I’m not really looking to select anything, I just want to update the users table by referencing it though the messages table, which is in turn being referenced by NEW.messageId

Answer 1

I do not know of there being a way to insert a select statement into a trigger. However, you can use the following syntax if you are looking to monitor for changes in a user’s score:

CREATE TRIGGER score_update
    BEFORE UPDATE ON score_table
    REFERENCING NEW ROW AS n, OLD ROW AS o
    FOR EACH ROW
    IF n.score <> o.score
    THEN
    END IF;
;