    # File lib/active_record/connection_adapters/mysql_adapter.rb, line 593
            def quoted_columns_for_index(column_names, options = {})
              length = options[:length] if options.is_a?(Hash)

              quoted_column_names = case length
              when Hash
                column_names.map {|name| length[name] ? "#{quote_column_name(name)}(#{length[name]})" : quote_column_name(name) }
              when Fixnum
                column_names.map {|name| "#{quote_column_name(name)}(#{length})"}
              else
                column_names.map {|name| quote_column_name(name) }
              end
            end