MyBatis与mysql一对一以及多对多查询

<?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.ask.mapper.OrderMapper">
<!-- 订单 -->
<resultMap type="com.ask.pojo.Order" id="order1">
<id column="id" property="id"/>
<result column="user_id" property="user_id"/>
<result column="number" property="number"/>
<result column="createTime" property="createTime"/>
<result column="note" property="note"/>
<!-- 一对一关系映射 -->
<association property="user" javaType="com.ask.pojo.User">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="address" property="address"/>
</association>

</resultMap>
<!-- 订单多对多 -->
<resultMap type="com.ask.pojo.Order" id="order2" extends="order1">
<!-- <id column="id" property="id"/>
<result column="user_id" property="user_id"/>
<result column="number" property="number"/>
<result column="createTime" property="createTime"/>
<result column="note" property="note"/>
<association property="user" javaType="com.ask.pojo.User">
<id column="id" property="id"/>
<result column="username" property="username"/>
<result column="address" property="address"/>
</association> -->
<!-- 多对多关系 -->
<collection property="orderdetails" ofType="com.ask.pojo.Orderdetail">
<id column="orderdetail_id" property="id"/>
<result column="items_id" property="items_id"/>
<result column="items_num" property="items_num"/>
</collection>

</resultMap>

<select id="getOrderAndUser" resultMap="order1">
SELECT
orders.*,
user.username,
user.address
FROM
orders, user
WHERE orders.user_id = user.id
</select>

<select id="getOrderAndUser1" resultMap="order2">
SELECT
orders.*,
user.username,
user.address,
orderdetail.id orderdetail_id,
orderdetail.items_id,
orderdetail.items_num
FROM
orders,USER,orderdetail

WHERE orders.user_id = user.id
AND orders.id = orderdetail.orders_id
</select>
</mapper>