Hvordan udfører jeg forespørgsler ved DB-forbindelse i Rails?

Rails bruger forbindelsespooling, så dit bedste bud er at bruge en alias_method_chain til ActiveRecord::ConnectionAdapters::ConnectionPool#new_connection

module ActiveRecord
  Module ConnectionAdapters
    class ConnectionPool
      alias_method_chain :new_connection, :my_stuff
      private
      def new_connection_with_my_stuff
        c = new_connection_without_my_stuff
        # Do your stuff with 
        # c.exec(<your sql command>)
        c
      end
    end
  end
end