按日分组：select DATE_FORMAT(o.OrderDate,'%Y%m%d') weeks,count(*) count from orders o group by weeks;
按月分组：select DATE_FORMAT(o.OrderDate,'%Y%m') weeks,count(*) count from orders o group by weeks;
按周分组： select DATE_FORMAT(o.OrderDate,'%Y_%u') weeks,count(*) count from orders o group by weeks;
按季度分组：select CONCAT(YEAR(o.OrderDate),'_',quarter(o.OrderDate)) qu,count(*) count from orders o group by qu;
