-- Group announcement (owner/admin) and per-member remark (self only).

ALTER TABLE `groups`
    ADD COLUMN announcement VARCHAR(1024) NOT NULL DEFAULT '' COMMENT '群公告，仅群主/管理员可改' AFTER avatar;

ALTER TABLE group_members
    ADD COLUMN remark VARCHAR(32) NOT NULL DEFAULT '' COMMENT '成员对该群的备注，仅自己可见' AFTER nickname;