mybatis sql 子查询 collection

mybatis sql中的子查询collection是通过在resultMap中使用collection标签来实现的。在子查询collection中，我们可以指定一个属性，该属性是一个集合类型，用来存储子查询的结果。在子查询中，我们可以指定子查询的类型、javaType和resultMap等信息。

在给定的引用内容中，并没有提及具体的子查询collection的使用例子和相关细节，因此我无法提供更多详细的信息。如果您有关于mybatis sql子查询collection的更具体的问题，请提供更多细节或相关的示例代码，我将尽力为您解答。

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mybatis collection 子查询

MyBatis allows you to perform collection subqueries, which can be useful when you need to retrieve related data for a collection of records. Collection subqueries are typically used in scenarios where you have a one-to-many or many-to-many relationship between tables.

To implement a collection subquery in MyBatis, you can use the `<collection>` element within your result mapping. Here's an example:

<resultMap id="userMap" type="User">
  <id property="id" column="user_id" />
  <result property="name" column="user_name" />
  <collection property="orders" ofType="Order">
    <id property="id" column="order_id" />
    <result property="product" column="product_name" />
  </collection>
</resultMap>

In this example, we have a `User` object that has a collection of `Order` objects. The `User` object has an `id` and a `name`, while the `Order` object has an `id` and a `product`. The `collection` element is used to define the mapping for the collection property (`orders`) of the `User` object.

To perform the collection subquery, you can use the `<select>` element with a nested `<collection>` element in your SQL statement. Here's an example:

<select id="getUserWithOrders" resultMap="userMap">
  SELECT u.id AS user_id, u.name AS user_name,
         o.id AS order_id, o.product AS product_name
  FROM users u
  INNER JOIN orders o ON u.id = o.user_id
  WHERE u.id = #{userId}
</select>

In this example, we join the `users` and `orders` tables on the `user_id` column and retrieve the relevant columns for both the `User` and `Order` objects. The `<collection>` element is used to map the query results to the collection property (`orders`) of the `User` object.

You can then use this mapping and SQL statement in your MyBatis mapper interface to retrieve a `User` object with its associated `Order` objects.

I hope this explanation helps! Let me know if you have any further questions.

mybatis中foreach的collection属性，怎么设置成另一个sql查询结果

MyBatis 中的 `<foreach>` 标签可以用于遍历集合或数组，并将遍历得到的元素作为参数传递给 SQL 语句中的 IN 子句，例如：

<select id="getUserByIds" resultType="User">
  SELECT * FROM users WHERE id IN
  <foreach item="id" collection="ids" open="(" separator="," close=")">
    #{id}
  </foreach>
</select>

在上面的示例中，`<foreach>` 标签的 `collection` 属性指定了遍历的集合或数组，`item` 属性指定了遍历得到的元素的名称，`open` 属性指定了 IN 子句的左括号，`separator` 属性指定了元素之间的分隔符，`close` 属性指定了 IN 子句的右括号，`#{id}` 表示使用遍历得到的元素作为参数传递给 SQL 语句中的占位符。

如果想要将 `<foreach>` 标签的 `collection` 属性设置为另一个 SQL 查询的结果，可以使用 MyBatis 提供的子查询语法，例如：

<select id="getUsersByDeptIds" resultType="User">
  SELECT * FROM users WHERE dept_id IN
  (SELECT id FROM depts WHERE name = #{deptName})
</select>

在上面的示例中，`dept_id IN` 后面的子查询语句使用了另一个 SQL 查询的结果来作为参数传递给 IN 子句。