如何在聚合列上使用ORDER BY

Question

这是我的mysql声明：

select distinct(prodname), 
       sum(qty) 
from tblordertrail 
group by prodname;

结果是：

+----------+------------+
| prodname |  sum(qty)  |
+----------+------------+
| product1 |  27        |
| product2 |  77        |
| product3 |  198       |
| product4 |  34        |
+----------+------------+

但我想要的结果是：

+----------+------------+
| prodname |  sum(qty)  |
+----------+------------+
| product3 |  198       |
| product2 |  77        |
| product4 |  34        |
| product1 |  27        |
+----------+------------+

先谢谢我的同事们。