mysql 查询N个分类下的前N条数据

@N = 分类数
@R = 分类下的记录数

SELECT a.* 
    FROM link_audio_label AS a,
    (SELECT GROUP_CONCAT(audio_id ORDER BY audio_id desc) aids FROM link_audio_label GROUP BY label_id) b 
WHERE FIND_IN_SET(a.audio_id,b.aids) BETWEEN 1 AND @N LIMIT @N*@R