如何解决mybatis查询结果接收不同的问题

SELECT
b.operator_id,
b.class_count,
b.class_study,
b.student_count,
b.rownum AS rank,
b.rownum AS praiseSum
FROM
(
SELECT
concat((@rownum :=@rownum + 1) + 0, '') AS rownum,
operator_id,
class_count,
class_study,
student_count
FROM
(SELECT @rownum := 0) AS foo,
appraise_list
WHERE
base_id = 120
ORDER BY
class_count DESC
) b
WHERE
b.operator_id = 233