mybatis 多表查询 与配置

<?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">
<!--绑定一个对应的Dao/Mapper接口-->

<mapper namespace="com.liu.dao.StudentMapper">
    <select id="getStudents" resultType="student">
        select s.id,s.u_name,s.tid,t.t_name from student s,teacher t  where s.tid=t.id;
    </select>



    <resultMap id="studentTeacher" type="Student">
        <result column="id" property="id" />
        <result column="u_name" property="u_name" />
        <result column="tid" property="tid" />
        <association property="teacherss" column="tid" javaType="Teacher" select="getTeacher" />
    </resultMap>
    <select id="getStudents2" resultMap="studentTeacher">
        select * from student;
    </select>
    
    
    

    <resultMap id="studentTeacher3" type="Student">
        <result column="sid" property="id" />
        <result column="uname" property="u_name" />
        <result column="tid" property="tid" />
        <association property="teacherss"  javaType="Teacher">
            <result property="t_name" column="tname"></result>
        </association>
    </resultMap>
    <select id="getStudents3" resultMap="studentTeacher3">
        select s.id sid ,s.u_name uname,s.tid tid,t.t_name tname from student s,teacher t  where tid=t.id;
    </select>





    
    <select id="getTeacher" resultType="Teacher">
        select * from teacher  where id= #{id};
    </select>

</mapper>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
    <properties resource="db.properties" />

    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
        <package name="com.liu.pojo" />
    </typeAliases>


    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
<!--绑定接口-->
    <mappers>
        <package name="com.liu.dao"/>
    </mappers>

</configuration>