Question

so i’ve edited my code
i had this problem in another trigger but this time even changing WHERE clause doesn’t help

DELIMITER $$

CREATE TRIGGER pic_album_change  AFTER UPDATE  ON pictures
  FOR EACH ROW BEGIN
    UPDATE albums SET counter = counter + 1 WHERE albums.id = NEW.album_id;
    UPDATE albums SET counter = counter - 1 WHERE albums.id = OLD.album_id;


END $$
DELIMITER ;

error :

    <p>Error Number: 1442</p><p>Can't update table 'pictures' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

i dont see any changes on the pictures table in this trigger

i have another trigger that involves these two tables

DELIMITER $$
CREATE TRIGGER  album_change
  AFTER UPDATE
  ON albums
  FOR EACH ROW
BEGIN
  UPDATE pictures
     SET

      level = NEW.level


    WHERE
   pictures.album_id =  NEW.id   ;


END $$
DELIMITER ;

Answer 1

Your WHERE clause is the wrong way round.

WHERE albums.id = NEW.album_id 

would cause albums.counter to be incremented (presumably that’s the number of pictures in each album).

It matters because joins on tables are not commutative — the direction of the join is important. Here you need to find the record in albums to update based on the value of the row in pictures.

While in this case there isn’t really any ambiguity, SQL needs to follow rules about joins.

---

The issue with your second trigger is that MySQL is preventing a continuous cycle of updates. You have a trigger pic_album_change which updates albums when pictures is updated. And you have a trigger album_change which updates pictures when albums is updated. Those triggers will trigger each other.

It seems to me that the database design may need to be changed. Do you really need albums.counter when that data can be found with SELECT count(*) FROM pictures WHERE album_id=...? It should be possible to normalise data so that there no circular references in triggers. In fact triggers may not be necessary at all.