请给出三张数据表，并且用mybatis完成最基础的增删改查以及联合查询，批量删除等功能

好的，以下是三张数据表的示例以及使用MyBatis实现的基础增删改查和联合查询、批量删除等功能。

1. 用户表（user）

| 字段名 | 类型 | 描述 |
| --------- | --------- | -------- |
| id | int | 用户ID |
| username | varchar | 用户名 |
| password | varchar | 密码 |
| email | varchar | 邮箱 |
| created_at| timestamp | 创建时间 |

<!-- UserMapper.xml -->
<mapper namespace="com.example.mapper.UserMapper">
  
  <!-- 基础查询 -->
  <select id="getUserById" parameterType="int" resultType="com.example.model.User">
    SELECT * FROM user WHERE id = #{id}
  </select>
  
  <insert id="insertUser" parameterType="com.example.model.User">
    INSERT INTO user(username, password, email, created_at)
    VALUES(#{username}, #{password}, #{email}, #{createdAt})
  </insert>
  
  <update id="updateUser" parameterType="com.example.model.User">
    UPDATE user SET username = #{username}, password = #{password}, email = #{email}
    WHERE id = #{id}
  </update>
  
  <delete id="deleteUserById" parameterType="int">
    DELETE FROM user WHERE id = #{id}
  </delete>
  
  <!-- 联合查询 -->
  <select id="getUserOrders" parameterType="int" resultType="com.example.model.User">
    SELECT u.*, o.order_no, o.total_price FROM user u
    LEFT JOIN orders o ON u.id = o.user_id
    WHERE u.id = #{id}
  </select>
  
  <!-- 批量删除 -->
  <delete id="deleteUsers" parameterType="java.util.List">
    DELETE FROM user WHERE id IN
    <foreach collection="list" item="id" open="(" separator="," close=")">
      #{id}
    </foreach>
  </delete>

</mapper>

2. 商品表（product）

| 字段名 | 类型 | 描述 |
| --------- | --------- | -------- |
| id | int | 商品ID |
| name | varchar | 商品名 |
| price | decimal | 价格 |
| stock | int | 库存 |
| created_at| timestamp | 创建时间 |

<!-- ProductMapper.xml -->
<mapper namespace="com.example.mapper.ProductMapper">
  
  <!-- 基础查询 -->
  <select id="getProductById" parameterType="int" resultType="com.example.model.Product">
    SELECT * FROM product WHERE id = #{id}
  </select>
  
  <insert id="insertProduct" parameterType="com.example.model.Product">
    INSERT INTO product(name, price, stock, created_at)
    VALUES(#{name}, #{price}, #{stock}, #{createdAt})
  </insert>
  
  <update id="updateProduct" parameterType="com.example.model.Product">
    UPDATE product SET name = #{name}, price = #{price}, stock = #{stock}
    WHERE id = #{id}
  </update>
  
  <delete id="deleteProductById" parameterType="int">
    DELETE FROM product WHERE id = #{id}
  </delete>
  
  <!-- 联合查询 -->
  <select id="getProductOrders" parameterType="int" resultMap="com.example.mapper.ProductMapper.ProductOrderResultMap">
    SELECT p.*, o.order_no, o.total_price FROM product p
    LEFT JOIN order_item oi ON p.id = oi.product_id
    LEFT JOIN orders o ON oi.order_id = o.id
    WHERE p.id = #{id}
  </select>
  
  <resultMap id="ProductOrderResultMap" type="com.example.model.Product">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="price" column="price"/>
    <result property="stock" column="stock"/>
    <collection property="orders" ofType="com.example.model.Order">
      <id property="orderNo" column="order_no"/>
      <result property="totalPrice" column="total_price"/>
    </collection>
  </resultMap>
  
  <!-- 批量删除 -->
  <delete id="deleteProducts" parameterType="java.util.List">
    DELETE FROM product WHERE id IN
    <foreach collection="list" item="id" open="(" separator="," close=")">
      #{id}
    </foreach>
  </delete>

</mapper>

3. 订单表（orders）

| 字段名 | 类型 | 描述 |
| --------- | --------- | -------- |
| id | int | 订单ID |
| order_no | varchar | 订单号 |
| user_id | int | 用户ID |
| total_price| decimal | 总价 |
| created_at| timestamp | 创建时间 |

<!-- OrderMapper.xml -->
<mapper namespace="com.example.mapper.OrderMapper">
  
  <!-- 基础查询 -->
  <select id="getOrderById" parameterType="int" resultType="com.example.model.Order">
    SELECT * FROM orders WHERE id = #{id}
  </select>
  
  <insert id="insertOrder" parameterType="com.example.model.Order">
    INSERT INTO orders(order_no, user_id, total_price, created_at)
    VALUES(#{orderNo}, #{userId}, #{totalPrice}, #{createdAt})
  </insert>
  
  <update id="updateOrder" parameterType="com.example.model.Order">
    UPDATE orders SET order_no = #{orderNo}, user_id = #{userId}, total_price = #{totalPrice}
    WHERE id = #{id}
  </update>
  
  <delete id="deleteOrderById" parameterType="int">
    DELETE FROM orders WHERE id = #{id}
  </delete>
  
  <!-- 联合查询 -->
  <select id="getOrderItems" parameterType="int" resultMap="com.example.mapper.OrderMapper.OrderItemResultMap">
    SELECT oi.quantity, oi.price, p.* FROM order_item oi
    LEFT JOIN product p ON oi.product_id = p.id
    WHERE oi.order_id = #{id}
  </select>
  
  <resultMap id="OrderItemResultMap" type="com.example.model.Order">
    <id property="id" column="id"/>
    <result property="quantity" column="quantity"/>
    <result property="price" column="price"/>
    <association property="product" javaType="com.example.model.Product">
      <id property="id" column="id"/>
      <result property="name" column="name"/>
      <result property="price" column="price"/>
      <result property="stock" column="stock"/>
    </association>
  </resultMap>
  
  <!-- 批量删除 -->
  <delete id="deleteOrders" parameterType="java.util.List">
    DELETE FROM orders WHERE id IN
    <foreach collection="list" item="id" open="(" separator="," close=")">
      #{id}
    </foreach>
  </delete>

</mapper>