public class tbl_dept {
    private int id;
    private String deptName;
  
//自己添加get和set方法
}

public class tbl_employee {
    private  int id;
    private String userName;
    private String gender;
    private String email;
    private int dId;
    private tbl_dept dept;//声明了一个tbl_dept 对象

//自己添加get和set方法 }

public interface Tbl_employeeMapper {
    public tbl_employee findTblEmployeeById(int id);

}

 <resultMap type="com.neuedu.bean.tbl_employee" id="findTblEmployeeByIdMap">
        <id  column="id" property="id" />
        <result column="email" property="email" />
        <result column="gender" property="gender" />
        <result column="user_name" property="userName" />
        <result column="d_id" property="dId"/>
　　　　　<!-- property 属性指定的POJO中关联的其它POJO在本POJO中的属性，JavaType指定的是关联的POJO的全类名-->
　　　　　　<!--id 用于指定主键，result用于指定普通的字段，column用于指定数据库字段，property用于指定POJO中的属性 -->
        <association property="dept" javaType="com.neuedu.bean.tbl_dept">
            <id column="id" property="id"/>
            <result column="dept_name" property="deptName"/>
        </association>
    </resultMap>
<select id="findTblEmployeeById" resultMap="findTblEmployeeByIdMap" parameterType="int">
        select e.id,e.email,e.gender,e.user_name,e.d_id,d.id did,d.dept_name
        from tbl_employee e ,tbl_dept d <!-- 这里使用了别名-->
        where  e.id=#{id} and d.id=e.id
    </select>

<resultMap type="com.neuedu.bean.tbl_employee" id="findTblEmployeeByIdMap">
        <id  column="id" property="id" />
        <result column="email" property="email" />
        <result column="gender" property="gender" />
        <result column="user_name" property="userName" />
        <result column="d_id" property="dId"/>
        <result column="did" property="dept.id"/>
        <result column="dept_name" property="dept.deptName"/>
    </resultMap>
<select id="findTblEmployeeById" resultMap="findTblEmployeeByIdMap" parameterType="int">
        select e.id,e.email,e.gender,e.user_name,e.d_id,d.id did,d.dept_name
        from tbl_employee e ,tbl_dept d
        where  e.id=#{id} and d.id=e.id
    </select>

　　　<select id="selectDepartment" resultType="com.neuedu.bean.tbl_dept">
        select * from tbl_dept where id=#{id}
    </select>
    <resultMap type="com.neuedu.bean.tbl_employee" id="findTblEmployeeByIdMap">
        <id  column="id" property="id" />
        <result column="email" property="email" />
        <result column="gender" property="gender" />
        <result column="user_name" property="userName" />
    　　　　<!-- select指定上面的statement语句的id  column指定的是上面的查询语句的需要的参数   -->
        <association property="dept" select="selectDepartment" column="d_id"></association>
    </resultMap>
    
    
        
    <select id="findTblEmployeeById" resultMap="findTblEmployeeByIdMap" parameterType="int">
        select e.id,e.email,e.gender,e.user_name,e.d_id
        from tbl_employee e
        where  e.id=#{id}
    </select>