# File lib/aws/simple_db/item_collection.rb, line 485
      def where_clause
        all_conditions = conditions.dup
        if @not_null_attribute
          all_conditions << coerce_attribute(@not_null_attribute) + " IS NOT NULL"
        end
        if all_conditions.empty?
          ""
        else
          " WHERE " + all_conditions.join(" AND ")
        end
      end