From PHPBB用户手册

# Table: 'phpbb_user_group'
CREATE TABLE phpbb_user_group (
	group_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 用户组ID
	user_id mediumint(8) UNSIGNED DEFAULT '0' NOT NULL, 用户ID
	group_leader tinyint(1) UNSIGNED DEFAULT '0' NOT NULL, 是否是组领导
	user_pending tinyint(1) UNSIGNED DEFAULT '1' NOT NULL, 是否在等待批准
	KEY group_id (group_id),
	KEY user_id (user_id),
	KEY group_leader (group_leader)
) CHARACTER SET `utf8` COLLATE `utf8_bin`;