一條SQL語句怎麼求環比！這個月簡曆數減去上個月的（如圖）

一條SQL語句如何求環比！這個月簡曆數減去上個月的（）

【這個月簡曆數】-【上個月的簡曆數】=【環比數】（）

sql語句如何寫？
SELECTDATE_FORMAT(m_adddate,'%m') as month,count(m_id) as zong,DATE_FORMAT(m_adddate,'%Y') as year from job_myreceive where DATE_FORMAT(m_adddate,'%Y')=2011 GROUP BY DATE_FORMAT(m_adddate,'%m');

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------解決方案--------------------
嗯，這樣寫清楚些

SELECT DATE_FORMAT(a.m_adddate,'%Y%m') as Ym, count(*) as `當月`,
(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     當月   上月  
201012 6      0 
201101 2      6 
201105 1      0 
201107 2      0 
201112 1      0 
201305 1      0

