额，我已经解决了，贴给大家看一看，关键是同时ORDER BY日期和人，写完了发现还是很简单的...

    <select id="getUserVisitDoListDistinct" parameterClass="java.util.Map" resultMap="userVisitDoResult">
        SELECT
            id,
            user_id_to,
            user_id_from,
            status,
            MAX(createtime) AS createtime 
        FROM
            (select * from dx_user_visit ORDER BY createtime DESC) AS foo 
        WHERE user_id_to = #user_id_to# AND user_id_from != #user_id_to#
        GROUP BY (DATE_FORMAT(createtime,"%Y%m%d")),user_id_from
        <isGreaterThan prepend="HAVING" property="lastId" compareValue="0">
           <![CDATA[
               id < #lastId# 
           ]]> 
        </isGreaterThan>
        ORDER BY createtime DESC
        LIMIT 0,#count#
    </select>

从访问中选择 v1.* 作为 v1
右连接（
按 id 从访问组中选择 id, max(createtime) 作为 ctime
）作为 v1.id=v2.id 和 v1 上的 v2 .createtime=v2.ctime

从访问中选择 v1.* 作为 v1
右连接（
从访问中选择 vv1.id, max(vv1.createtime) 作为 ctime 作为 vv1
内部连接在 vv1.DATE_FORMAT 上作为 vv2 访问（ createtime,"%Y%m%d")=vv2..DATE_FORMAT(createtime,"%Y%m%d")
group by vv1.id
) as v2 on v1.id=v2.id和 v1.createtime=v2.ctime

select user_id_from, min(createtime) last_visit_time from tablename group by user_id_from order by last_visit_time limit num;

select max time from tb group by usrid这样如何