在mysql中group by week 日统计 月统计

易客CRM之前的版本中有一个报表是按月统计销售情况，最近有个客户想按周统计销售情况。按月统计的Sql语句比较好写，sql语句如下：
SELECT DATE_FORMAT(ec_salesorder.duedate,’%Y-%m’) as m, sum(ec_salesorder.total) as total, count(*) as so_count FROM ec_salesorder GROUP BY m ORDER BY m，也就是把duedate日期以月的形式显示，然后groupby，那么按周如何统计呢？
搜了一下mysql的manual，在这里(http://lists.mysql.com/mysql/2664)找 到一个解决方法，通过mysql的week函数来做，sql语句如下：SELECT WEEK(ec_salesorder.duedate) as m, sum(ec_salesorder.total) as total, count(*) as so_count FROM ec_salesorder GROUP BY m ORDER BY m，这个方法有个缺陷，不能显示年份，仅仅靠一个周数不方便查看统计信息。
继续研究mysql manual，在DATE_FORMAT函数介绍发现2个格式符和周有点关系：
%X Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V
%x Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v
把上面的Sql语句中改成：
SELECT DATE_FORMAT(ec_salesorder.duedate,’%x %v’) as m, sum(ec_salesorder.total) as total, count(*) as so_count FROM ec_salesorder GROUP BY m ORDER BY m
显示的结果如下：
m total so_count
2009 11 10000.00 3
2009 12 44000.00 5
如果周日为一周的第一天，那么sql语句应该为:
SELECT DATE_FORMAT(ec_salesorder.duedate,’%X %V’) as m, sum(ec_salesorder.total) as total, count(*) as so_count FROM ec_salesorder GROUP BY m ORDER BY m
结果应该没错，不出意外，易客CRM下个版本将增加按周统计销售情况的报表