    # File lib/active_record/connection_adapters/postgresql_adapter.rb, line 321
          def add_column(table_name, column_name, type, options = {})
            default = options[:default]
            notnull = options[:null] == false

            # Add the column.
            execute("ALTER TABLE #{table_name} ADD COLUMN #{column_name} #{type_to_sql(type, options[:limit])}")

            # Set optional default. If not null, update nulls to the new default.
            if options_include_default?(options)
              change_column_default(table_name, column_name, default)
              if notnull
                execute("UPDATE #{table_name} SET #{column_name}=#{quote(default, options[:column])} WHERE #{column_name} IS NULL")
              end
            end

            if notnull
              execute("ALTER TABLE #{table_name} ALTER #{column_name} SET NOT NULL")
            end
          end