当实体类属性与表中列名不一样时,需要定义resultMap,否则查询对象为空
resultMap id="person" type="Person">
<result property="username" column="name"></result>
<result property="password" column="age"></result>
</resultMap>
resultMap id="person" type="Person">
<result property="username" column="name"></result>
<result property="password" column="age"></result>
</resultMap>