gistfile1.txt

Migration: 

class CreateOutboundRates < ActiveRecord::Migration
  def self.up
    create_table :outbound_rates do |t|
      t.string :destination
      t.integer :prefix
      t.integer :rate_in_cents
      t.timestamps
    end

    add_index :outbound_rates, :prefix
  end

  def self.down
    drop_table :outbound_rates
  end
end

Model:
class OutboundRate < ActiveRecord::Base
  money :rate
end

Task:

I need a finder function that will take any arbitrary number and return the most specific match based on prefix in the most efficient manner possible (there are 16,000 records).

Example records:
[1] ALGERIA - MOBILE - MOBILIS,21366,0.1784
[2] ALGERIA - MOBILE - MOBILIS,213697,0.1784
[3] ALGERIA - MOBILE - MOBILIS,213698,0.1784
[4] ALGERIA - MOBILE - ORASCOM,21391,0.2057

So if given the number 21366234324 it would match record number 1, if given 2136973432 it would match record number 2.