mybatis 多对一

<?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.cj.dao.StudentMapper">


    <resultMap id="studentTeacher2" type="student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="teacher">
            <result property="name" column="tname"/>
            <result property="id" column="tid"/>
        association>
    resultMap>

    <select id="getStudents2" resultMap="studentTeacher2">
        select s.id sid,s.name sname,t.id tid,t.name tname from mybatis.student s,mybatis.teacher t where s.tid = t.id;
    select>


    <resultMap id="studentTeacher" type="student">
        <association property="teacher" column="tid" javaType="teacher" select="getTeacher"/>
    resultMap>
    <select id="getStudents" resultMap="studentTeacher">
        select * from mybatis.student;
    select>

    <select id="getTeacher" resultType="teacher">
        select * from mybatis.teacher where id = #{tid};
    select>

mapper>