    # File lib/active_record/connection_adapters/abstract/schema_statements.rb, line 186
          def add_index(table_name, column_name, options = {})
            column_names = Array(column_name)
            index_name   = index_name(table_name, :column => column_names)

            if Hash === options # legacy support, since this param was a string
              index_type = options[:unique] ? "UNIQUE" : ""
              index_name = options[:name] || index_name
            else
              index_type = options
            end
            quoted_column_names = column_names.map { |e| quote_column_name(e) }.join(", ")
            execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{quoted_column_names})"
          end