Rails how to sum columns?

问题

Example I have:

@test = Pakke.find([[4], [5]])

In my Pakke table I have a column named prismd

How do I sum the two values for the prismd columns for @test?

回答1:

You can summarize directly on the database by creating the respective SQL like this:

Pakke.sum(:prismd, :conditions => {:id => [4,5]})

See ActiveRecord::Calculations for more usage examples and general documentation.

回答2:

ActiveRecord has a bunch of built-in calculation methods, including sum:

@test = Pakke.where(:id => [4, 5] ).sum(:prismd)

回答3:

Pakke.find([[14], [15]]).map(&:prismd).sum

回答4:

test = Order.where(potential_student_id: potential_student.id).sum("total_price");

来源：https://stackoverflow.com/questions/8874291/rails-how-to-sum-columns