一对多的某个情况

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qin.repository.ClassesRepository">
    <resultMap id="classesMap" type="com.qin.entity.Classes">
        <id column="id" property="id"/>
        <result column="classname" property="className"/>
        <collection property="students" ofType="com.qin.entity.Student" column="s">
            <id column="sid" property="id"/>
            <result column="sname" property="name"/>
            <result column="sage" property="age"/>
        </collection>
    </resultMap>
    <select id="findById" parameterType="int" resultMap="classesMap">
        select c.*,s.id as sid,s.name as sname,s.age as sage
                from t_class c
                  join t_student s
                 on c.id =2 and s.cid =2;
    </select>
</mapper>