mybatis多表联查练习题

Sure! Here's a practice question for performing multi-table joins with MyBatis:

Suppose we have two tables: "users" and "orders". The "users" table has the following columns: user_id, username, and email. The "orders" table has the following columns: order_id, user_id, order_date, and total_amount.

Write a MyBatis XML mapper query that retrieves all orders along with their corresponding user information (username and email).

<!-- Define a result map to map the query results to a POJO -->
<resultMap id="OrderUserResultMap" type="com.example.OrderUser">
  <id property="orderId" column="order_id"/>
  <result property="orderDate" column="order_date"/>
  <result property="totalAmount" column="total_amount"/>
  <result property="username" column="username"/>
  <result property="email" column="email"/>
</resultMap>

<!-- Write the mapper query -->
<select id="getOrdersWithUsers" resultMap="OrderUserResultMap">
  SELECT o.order_id, o.order_date, o.total_amount, u.username, u.email
  FROM orders o
  INNER JOIN users u ON o.user_id = u.user_id
</select>

Assuming you have a Java class called `OrderUser` with corresponding getters and setters for the properties (orderId, orderDate, totalAmount, username, email), you can use this query to retrieve all orders along with their user information.

Please make sure to modify the table names and column names according to your actual database schema. Let me know if you need any further assistance!