表名：product
表结构：
表数据：
如果使用日期查询的话：
sql： SELECT QUARTER(create_time) AS ‘季度‘,AVG(seller) AS ‘平均值‘ FROM product GROUP BY QUARTER(create_time);
如果按月份查询的话：
sql：SELECT FLOOR((mouth+2)/3) AS ‘季度‘,AVG(seller)AS‘平均值‘ FROM product GROUP BY FLOOR((mouth+2)/3);
原文：http://www.cnblogs.com/peasana/p/6612345.html