我的 MySQL 触发器不工作，语法简单，不复杂

I don't know why my trigger isn't working, the query works when I use it manually, but when I want to be updated by a trigger it doesn't work. Can someone help me to know why?

这是我的触发器:

    CREATE TRIGGER `upd_PTS` AFTER UPDATE ON `pos_table`
 FOR EACH ROW BEGIN
    IF (NEW.played_games <> OLD.played_games)
    THEN  
        update pos_table set PTS=((NEW.won_games*2)+(NEW.tie_games*1));
    END IF;
END

简单，这是一个体育锦标赛，当统计人员捕获比赛的分数时，他会自动添加一个played_game，并且分别是赢，平局或输球，所以我的触发器应该在他played_games改变时自动执行并且它有更改 PTS 列.但它不起作用.

update pos_table set PTS=((NEW.won_games*2)+(NEW.tie_games*1));