一条SQL语句怎么求环比！这个月简历数减去上个月的（如图）

SELECT DATE_FORMAT(a.m_adddate,'%Y%m') as Ym, count(*) as `当月`,
(select count(*) from job_myreceive where 
 DATE_FORMAT(a.m_adddate,'%Y%m') = DATE_FORMAT(DATE_add(m_adddate,INTERVAL 1 MONTH),'%Y%m')
) as 上月
 FROM job_myreceive a group by 1

Ym     当月   上月  
201012 6      0 
201101 2      6 
201105 1      0 
201107 2      0 
201112 1      0 
201305 1      0