建立公司产品数据库中产品销售表各地产品销售数量分类统计，再进行区域合计，最后进行总数合计的视图！应用建虚拟表，嵌套语句，union语句连接表等SQL语句实现-Establish product sales table in the database the number of categories throughout the sales statistics, then the region as a whole, the total number of final total for the