Mysql跨年按周彙總

先定義一個比較日期，如果周開始爲週日，那麼這天必須爲週日，如‘2014-03-23’

select date_add('2014-03-23',interval datediff(date,'2014-03-23') div 7*7 day) as week_start,  
date_add('2014-03-23',interval datediff(date,'2014-03-23') div 7*7+6 day)as week_end,sum(qty)
from table
group by datediff(date,'2014-03-23') div 7;