我想通过同时选择其他字段来将多个sums()链接到一个单独的组.我也更喜欢使用ActiveRecord方法来执行此操作,而不是手动构造一个sql字符串,因为我可以稍后修改继承的ActiveRecord类的行为.
例如,我想表示声明(举个例子)
select user_id,sum(cost) as total_cost,sum(quantity) as total_quantity from line_items group by user_id
有一些像：
LineItem.select(:user_id).group(:user_id).sum(:cost).sum(:quantity)
原因是我可能会在以后添加额外的分组和where-clause,这些都是共同的.
解决方法
这对我有用：
require "active_record" require "logger" ActiveRecord::Base.logger = Logger.new(STDOUT) ActiveRecord::Base.establish_connection :adapter => "postgresql",:database => "francois" ActiveRecord::Base.connection.execute "DROP TABLE IF EXISTS values" ActiveRecord::Base.connection.execute "CREATE TABLE values(user_id INTEGER NOT NULL,quantity INTEGER NOT NULL DEFAULT 1,cost INTEGER NOT NULL DEFAULT 2)" class Value < ActiveRecord::Base end 2.times do 5.times do |n| Value.create!(:user_id => n) end end Value.group(:user_id).select('user_id,SUM(cost) AS total_cost,SUM(quantity) AS total_quantity').each do |value| p [value.user_id,value.total_quantity,value.total_cost] end
我尝试了sum(：cost,：quantity),但是#sum不希望以这种方式定义参数.我也尝试了sum(：cost =>：total_cost,：quantity =>：total_quantity),没有用.