mybatis *Mapper.xml 中resultMap的id用來提高整體效能，是比較物件例項時的標識屬性，特別是嵌入快取和結果對映。如果resultMap中不含id項，有可能出現org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.TooManyResultsException: Expected one result (or null) to be returned by selectOne(), but found: 9

<select id="getStatisticData"
 
 parameterType="int" resultMap = "statisticResult">
        select p.ID PAPER_ID,p.TITLE,p.CONTENT,p.SUM_ANSWER,q.ID QUESTION_ID,q.TITLE QUESTION_TITLE,q.TYPE,
        i.ID QUESTION_ITEM_ID,i.TEXT,i.CHECKED_NUM 
        from paper p 
        left join question q on p.ID =  q.SURVEY_ID 
        left join question_item i on
 
 q.ID = i.QUESTION_ID 
        where p.ID = #{id}
    </select>
    <resultMap type="main.java.com.gazi.survey.bean.SurveyInfo" id="statisticResult">
        <id property = "id" column = "PAPER_ID"/>
        <association property ="paper" javaType = "Paper">
            <id property
 
 = "id" column = "PAPER_ID"/>
            <result property = "title" column = "TITLE"/>
            <result property = "content" column = "CONTENT"/>
            <result property = "sumAnswer" column = "SUM_ANSWER"/>
        </association>
        <collection property="questionInfoList" ofType = "main.java.com.gazi.survey.bean.SurveyInfo$QuestionInfo">
            <id property = "id" column = "QUESTION_ID"/>
            <association property = "question" javaType = "Question">
                <id property = "id" column = "QUESTION_ID"/>
                <result property = "title" column = "QUESTION_TYPE"/>
                <result property = "type" column = "TYPE"/>
            </association>
            <collection property="questionItemList" ofType = "QuestionItem">
                <id property = "id" column = "QUESTION_ITEM_ID"/>
                <result property = "text" column = "TEXT"/>
                <result property = "checkedNum" column = "CHECKED_NUM"/>
            </collection>
        </collection>
    </resultMap>

第一個ID數值一致保證了方法返回是POJO時也不會報多結果集異常，第二個QUESTION_ID確定了List中question物件2個，第三個QUESTION_ITEM_ID確定了每個question4個選項。