From PHPBB用户手册

用户参与话题信息
CREATE TABLE `phpbb_topics_posted` (
  `user_id` mediumint(8) unsigned NOT NULL default '0', //用户ID
  `topic_id` mediumint(8) unsigned NOT NULL default '0', //参与的话题ID
  `topic_posted` tinyint(1) unsigned NOT NULL default '0', // 0=否, 1=是
  PRIMARY KEY  (`user_id`,`topic_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_bin;