@gomorebug 解决了，在 UserHistory 添加成员变量 qid 和 uid ，在映射中也添加

@gomorebug id 搞错了，是这个
<select id="findHistoryByUid" resultMap="historyResultMap">
SELECT question.*, user.*, user_history.reply,user_history.h_updated,user_history.h_created,user_history.correct
FROM question,
user,
user_history
WHERE user.uid = #{uid}
AND user_history.uid = user.uid
AND user_history.qid = question.qid
</select>

主题中的查询语句
<select id="findQuestionsByUid" resultMap="questionResultMap">
SELECT question.*, user.*, user_history.reply,user_history.h_updated,user_history.h_created,user_history.correct
FROM question,
user,
user_history
WHERE user.uid = #{uid}
AND user_history.uid = user.uid
AND user_history.qid = question.qid
</select>

<resultMap id="questionResultMap" type="org.hugcode.common.pojo.User">
<id column="uid" property="uid"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
<result column="updated" property="updated"/>
<result column="created" property="created"/>
<collection property="questions" ofType="org.hugcode.common.pojo.Question">
<id column="qid" property="qid"/>
<result column="description" property="description"/>
<result column="answer" property="answer"/>
<result column="type" property="type"/>
</collection>

</resultMap>
<select id="findQuestionsByUid" resultMap="questionResultMap">
SELECT question.*,user.* FROM question,user,user_history WHERE user.uid = #{uid} AND user_history.uid = user.uid AND user_history.qid = question.qid
</select>


单纯在 User 类中一对多是没有问题的，但我想在关系表 user_history 保存用户的做题记录所以想新弄个实体类 UserHistory 存其他信息，结果就出现问题了😭，下面是包含关系
（ 1 ）正确：User ->List<Question>（ collection ）
（ 2 ）错误：User ->List<UserHistory> （ collection ）->Question （ association ）

@cpstar 受教了

@nulIptr 搜嘎

@liangkang1436 但这样不符合 client 和 server 的关系好像