mysql计算两个字段的积的总和

Question

$sql1 = "SELECT SUM(goods_amount*goods_user_rate) FROM " . $GLOBALS['ecs']->table('buy_info') . $where2;

goods_amount和good_user_rate是数据库的两个字段，请问正确的写法是怎样？

Answer 1

select sum(price * num) from table

Answer 2

SELECT SUM(ret) FROM(
SELECT goods_amount*goods_user_rate as ret FROM xxxx
);
我知道这样傻的写法是可以的。

Answer 3

select sum(price) * sum(num) as income from table