Sharding-jdbc分库分表后使用left join查询不到数据

原SQL：

    SELECT
    rm.id missionId,
    rpu.id paperUserId,
    rm.cover,
    if(rm.class_id is NULL,1,2) bookStatus,
    rm.`name`,
    DATE_FORMAT(rm.end_time,'%Y-%m-%d %H:%i:%s') endTime,
    rm.topic_id topicId,
    rm.create_user_id createUserId,
    IF(rue.id is NULL,1,2) missionStatus,
    rr.`level`
    FROM
    re_mission rm
    JOIN re_res rr on rr.fanya_res_id=rm.topic_id
    left JOIN re_user_evaluate rue ON rue.uid=rm.create_user_id and rue.topic_id=rm.topic_id
    left JOIN re_paper_user rpu on rpu.uid = #{param.uid} and rpu.topic_id=rm.topic_id and rpu.fid=rm.fid and rpu.is_max_lv=1
    WHERE
    ((rm.class_id = #{param.classId} AND rm.mission_type=2) OR (rm.create_user_id = #{param.uid} AND  rm.mission_type=1))
    and rm.publish_status in (1,3)  AND rm.fid = #{param.fid}
    GROUP BY rm.id
    ORDER BY rm.id DESC
    LIMIT #{param.startNumber},#{param.pageSize}

改造后SQL：

    SELECT
    rm.id missionId,
    MAX(if(rpu.id is NULL,0,rpu.id)) paperUserId,
    rm.cover,
    if(rm.class_id is NULL,1,2) bookStatus,
    rm.`name`,
    DATE_FORMAT(rm.end_time,'%Y-%m-%d %H:%i:%s') endTime,
    rm.topic_id topicId,
    rm.create_user_id createUserId,
    max(IF(rue.id is NULL,1,2)) missionStatus,
    rr.`level`
    FROM
    re_mission rm
    JOIN re_res rr on rr.fanya_res_id=rm.topic_id
    left JOIN re_user_evaluate rue ON rue.uid= #{param.uid}  and rue.topic_id=rm.topic_id
    left JOIN re_paper_user rpu on rpu.uid = #{param.uid} and rpu.topic_id=rm.topic_id and rpu.fid=rm.fid and rpu.is_max_lv=1
    WHERE
    ((rm.class_id = #{param.classId} AND rm.mission_type=2) OR (rm.create_user_id = #{param.uid} AND  rm.mission_type=1))
    and rm.publish_status in (1,3)  AND rm.fid = #{param.fid}
    GROUP BY rm.id
    ORDER BY rm.id DESC
    LIMIT #{param.startNumber},#{param.pageSize}

用了left join后要使用聚合函数取值，否则会被覆盖。