一对一、一对多的关联查询 ？

<mapper namespace="com.lcb.mapping.userMapper">    <!--association 一对一关联查询 -->    <select id="getClass" parameterType="int" resultMap="ClassesResultMap">        select * from class c,teacher t where c.teacher_id=t.t_id and        c.c_id=#{id}    </select>    <resultMap type="com.lcb.user.Classes" id="ClassesResultMap">        <!-- 实体类的字段名和数据表的字段名映射 -->        <id property="id" column="c_id"/>        <result property="name" column="c_name"/>        <association property="teacher" javaType="com.lcb.user.Teacher">        <id property="id" column="t_id"/>        <result property="name" column="t_name"/>        </association>    </resultMap>    <!--collection 一对多关联查询 -->    <select id="getClass2" parameterType="int" resultMap="ClassesResultMap2">        select * from class c,teacher t,student s where c.teacher_id=t.t_id        and c.c_id=s.class_id and c.c_id=#{id}    </select>    <resultMap type="com.lcb.user.Classes" id="ClassesResultMap2">        <id property="id" column="c_id"/>        <result property="name" column="c_name"/>        <association property="teacher" javaType="com.lcb.user.Teacher">        <id property="id" column="t_id"/>        <result property="name" column="t_name"/>    </association>    <collection property="student" ofType="com.lcb.user.Student">        <id property="id" column="s_id"/>        <result property="name" column="s_name"/>    </collection>    </resultMap></mapper>