-- One directed follow per pair. Mutual follows become friend edges in logic; unfollowing does not delete messages.

CREATE TABLE IF NOT EXISTS t_user_follows (
    id          BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增',
    user_id     BIGINT NOT NULL COMMENT '关注人 user_id',
    target_id   BIGINT NOT NULL COMMENT '被关注人 user_id',
    created_at  DATETIME(3) NOT NULL COMMENT '关注时间',
    PRIMARY KEY (id),
    UNIQUE KEY uk_user_target (user_id, target_id),
    KEY idx_target (target_id)
) COMMENT='单向关注。双方互相关注时写入已有双向好友边；取消关注只删关注，不再互关时删好友边，不删消息';