Rails 中相乘列的总和
这应该很容易。在 MySQL 中我可以这样做：
select sum(column1*column2) as sum1 from table
How do you do this in Rails with sqlite?我已经尝试过 find_by_sql 与上面的确切查询，以及 find(:all, :select=>...) 和各种其他东西，但没有一个返回正确的值。大多数都是空白的，就像这样：
[#<Element> ]
我可以循环遍历，取出值，然后求和，但必须这样做似乎很荒谬。
有人能指出我明显缺少的东西吗？谢谢！
This should be easy. In MySQL I could just do:
select sum(column1*column2) as sum1 from table
How do you do this in Rails with sqlite? I've tried find_by_sql with the exact query above, as well as find(:all, :select=>...), and all sorts of other things, but none return the proper value. Most are just blank, like this:
[#<Element> ]
I could loop through, pull out values, and then sum, but it seems absurd to have to do that.
Can someone point me to what I'm obviously missing? Thanks!
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http://ar.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html
http://ar.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html
正如 @glortho 在评论中所说，解决方案是
Element.sum( "column1*column2" )这甚至可以跨多个表使用
Foo.includes(:bars).references(:bars) .sum('foos.cost * Bars.available')SQL 令人难以置信！
As @glortho said in a comment, the solution is
Element.sum( "column1*column2" )This even works across multiple tables
Foo.includes(:bars).references(:bars).sum('foos.cost * bars.available')SQL IS INCREDIBLE!