order by 关键字详解:
SELECT intcode AS 商品编码, product_title AS 名称, retailprice AS 零售价, purchaseprice AS 合同进价 FROM product_detail WHERE brand='0063飘柔' AND purchaseprice>10 ORDER BY purchaseprice DESC;
desc是降序。升序关键字是
ASC,如果不写desc和ASC,默认是升序排列的

下面搞一搞中文别名排序:
SELECT intcode AS 商品编码, product_title AS 名称, retailprice AS 零售价, purchaseprice AS 合同进价 FROM product_detail WHERE brand='0063飘柔' AND purchaseprice>10 ORDER BY '零售价' DESC;
本来想按照中文别名来排序,但是输出竟然是按照默认的升序。看来order by 语句出错了,就不执行了

起个英文别名试试:
SELECT intcode AS 商品编码, product_title AS 名称, retailprice AS tt, purchaseprice AS 合同进价 FROM product_detail WHERE brand='0063飘柔' AND purchaseprice>10 ORDER BY tt DESC;
竟然成功了。而且测试发现tt还不能加单引号。

我靠,想想不对啊,我把中文别名也不加单引号试试。发现是我搞错了:
SELECT intcode AS 商品编码, product_title AS 名称, retailprice AS 零售价, purchaseprice AS 合同进价 FROM product_detail WHERE brand='0063飘柔' AND purchaseprice>10 ORDER BY 零售价 desc;
ORDER BY 零售价 desc 语句中的零售价是中文,不加单引号,也能排序!!

小结:(1)mysql对于执行顺序比较靠后的语句,如果出错了就不执行,而且不报错。
(2)按照查询出来的字段的别名排序也是可以的,不管别名是中文还是英文,只要不加单引号就行。