Question

I want to get the sums for a dozen columns in a table.

# 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

Is there a way to do this in one query? The above generates a dozen queries.

Answer 1

You could do something with manually overriding the select values like this, which would run a single query returning all of your sums as fields:

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