From PHPBB用户手册

# Table: 'phpbb_attachments' 论坛附件信息
CREATE TABLE phpbb_attachments (
	attach_id mediumint(8) UNSIGNED NOT NULL auto_increment, 附件ID, 用于唯一标识附件, 自增
	post_msg_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 附件隶属的帖子(短信)ID
	topic_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 附件隶属的主题ID, 当附件存在于短信中时, 这个值为0
	in_message tinyint(1) UNSIGNED DEFAULT '0' NOT NULL, 是否在站内短信中, 0表示不是
	poster_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 发表附件的用户ID
	is_orphan tinyint(1) UNSIGNED DEFAULT '1' NOT NULL, 是否是幽灵文件, 0表示不是
	physical_filename varchar(255) DEFAULT '' NOT NULL, 文件系统中存储的真实文件名
	real_filename varchar(255) DEFAULT '' NOT NULL, 文件的原文件名
	download_count mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 下载(浏览)次数
	attach_comment text NOT NULL, 附件注释
	extension varchar(100) DEFAULT '' NOT NULL, 扩展名
	mimetype varchar(100) DEFAULT '' NOT NULL, 数据类型
	filesize int(20) UNSIGNED DEFAULT '0' NOT NULL, 文件大小
	filetime int(11) UNSIGNED DEFAULT '0' NOT NULL, 文件修改时间
	thumbnail tinyint(1) UNSIGNED DEFAULT '0' NOT NULL, 是否有缩略图
	PRIMARY KEY (attach_id),
	KEY filetime (filetime),
	KEY post_msg_id (post_msg_id),
	KEY topic_id (topic_id),
	KEY poster_id (poster_id),
	KEY is_orphan (is_orphan)
) CHARACTER SET `utf8` COLLATE `utf8_bin`;