# File src/rails-1.2.2/activerecord/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