查找三张表中对应的数据字段，并连接起来

自我感觉和两张表的连接差不多（小白，刚刚学习Java不久，大佬勿喷）。
将三张表中分别取一两个对应数据连接起来。将其分为1，2，3。其中2为中间表，用来连接1，3表，2表中加入了字段
1.先在pojo中封装自己需要得到的几个类型
@TableId(value = "user_id",type = IdType.AUTO)
private Integer userId;
private String userName;
private String userPwd;
private String salt;
private String email;
private String phone;
@TableField(exist = false)
private String code;
//这是需要的对象，将他引入。 
@TableField(exist = false)
private List<Score> listScore;
@TableField(exist = false)
private List<Paper> listPaper;

2.在xml中将几个表的数据用collection（association)连接起来，column对应数据库中的命名，property对应列对象中的名字

<resultMap id="userInfoScorePaper" type="com.hqyj.pojo.UserInfo">
    <result column="user_id" property="userId" />
    <result column="user_name" property="userName" />
    <result column="user_pwd" property="userPwd" />
    <result column="salt" property="salt" />
    <result column="phone" property="phone" />
    <result column="email" property="email" />
    <collection property="listScore" ofType="com.hqyj.pojo.Score">
        <id column="score_id" property="scoreId"/>
        <result column="user_id" property="userId" />
        <result column="paper_id" property="paperId" />
        <result column="score" property="score" />
        <result column="save_time" property="saveTime" />
    </collection>
    <collection property="listPaper" ofType="com.hqyj.pojo.Paper">
        <id column="paper_id" property="paperId" />
        <result column="paper_name" property="paperName" />
        <result column="paper_score" property="paperScore" />
        <result column="paper_time" property="paperTime" />
    </collection>
</resultMap>

3.编写sql语句 （resultMap对应上方的id，并且这个id对应mapper也叫dao层方法名）

<select id="queryScoreByUserName" resultMap="userInfoScorePaper" parameterType="java.lang.String">
        SELECT u.user_name,s.score,p.paper_name,p.paper_score,s.save_time
FROM user_info u
INNER JOIN score s ON u.user_id = s.user_id
INNER JOIN paper p ON p.paper_id = s.paper_id
WHERE u.user_name =#{userName}
</select>