sql group by
有这么一句group by 语句
sql.Add('select sortno as 大类代码,sortname as 大类名称,clientno as 客户代码,clientname as 客户名称,sum(quantity2) as 销售小数量,sum(salessum) as 销售金额,sum(tax) as 销售税金 from '+vw1+' group by sortno,sortname,clientno,clientname');
期中变量vw1是一个表名,在delphi中运行该语句后,总是报“不是group by 表达式”,而如果我不用变量表名的话,就可以正常运行,请问这是什么原因