问题描述：

某用户主页访问表visit，用来记录用户个人主页被访问的记录。
字段有：

id user_id_from user_id_to time

现有查看用户主页访问记录的需求，去重需求为只保存某天内同一用户的最新一条的记录。

解决方法：

    <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>