问题
由于嵌套结果方式会导致结果集被折叠，因此分页查询的结果在折叠后总数会减少
<resultMap id="baseResultMap" type="com.jia.Student">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="gender" property="gender"/>
<collection property="bookList" ofType="com.jia.Book">
<result column="book_id" property="id"/>
<result column="student_id" property="studentId"/>
<result column="amount" property="amount"/>
</collection>
</resultMap>
<select id="getStudent" resultMap="baseResultMap">
SELECT
Student.id,
Student.`name`,
Student.gender,
book.id book_id,
book.student_id,
book.amount
FROM
student
left join book on book.student_id=student.id
WHERE
student.is_delete=0
limit
#{pageNumber} ,#{pageSize}
</select>
解决方法
使用collection里的select定义查询，条件是上层student的id
执行过程是，先执行getStudent的查询，将学生全都查询出来并进行分页，这种情况下分页是没问题的，然后再去查询每个学生对应的多条书本信息，走collection里的select查询，使用的条件是第一次查询结果中的主键id，然后他会自己查询book信息封装到每个对应的student中，完成查询。
<resultMap id="baseResultMap" type="com.jia.Student">
<id column="id" property="id"/>
<result column="name" property="name"/>
<result column="gender" property="gender"/>
<collection property="bookList" ofType="com.jia.Book" select="selectBook" column="id">
<result column="book_id" property="id"/>
<result column="student_id" property="studentId"/>
<result column="amount" property="amount"/>
</collection>
</resultMap>
<select id="getStudent" resultMap="baseResultMap">
SELECT
Student.id,
Student.`name`,
Student.gender
FROM
student
WHERE
student.is_delete=0
limit
#{pageNumber} ,#{pageSize}
</select>
<select id="selectBook" resultType="com.jia.Book">
select * from book where book.student_id=#{id}
</select>
