ruby-on-rails-3 - ruby on Rails 3 可以在一个查询中检索多列的总和吗？

Question

我想获得表中十几列的总和。

# result will be {:a => 340.5, :b => 21.8, ... }
# where :a has the sum of the :a column values
# entries is an ActiveRecord model, e.g. ScoreCard.where(:user => user)
def self.totals(entries)
  [:a, :b, :c, :d, :e, :f, :g, :h, :i, :j, :k, :m].inject({}) do |tv, col|
     tv[col] = entries.sum(col)
     tv
  end
end

有没有办法在一个查询中做到这一点？上面生成了十几个查询。

Answer 1

您可以通过手动覆盖 select 值来执行某些操作，如下所示，这将运行一个查询，将所有总和作为字段返回:

sums = entries.select("sum(a) as a, sum(b) as b, ....").first
tv[:a] = sums[:a]
tv[:b] = sums[:b]
# etc....