instance method change_column

# File activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb, line 820
      def change_column(table_name, column_name, type, options = {})
        quoted_table_name = quote_table_name(table_name)

        begin
          execute "ALTER TABLE #{quoted_table_name} ALTER COLUMN #{quote_column_name(column_name)} TYPE #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
        rescue ActiveRecord::StatementInvalid => e
          raise e if postgresql_version > 80000
          # This is PostgreSQL 7.x, so we have to use a more arcane way of doing it.
          begin
            begin_db_transaction
            tmp_column_name = "#{column_name}_ar_tmp"
            add_column(table_name, tmp_column_name, type, options)
            execute "UPDATE #{quoted_table_name} SET #{quote_column_name(tmp_column_name)} = CAST(#{quote_column_name(column_name)} AS #{type_to_sql(type, options[:limit], options[:precision], options[:scale])})"
            remove_column(table_name, column_name)
            rename_column(table_name, tmp_column_name, column_name)
            commit_db_transaction
          rescue
            rollback_db_transaction
          end
        end

        change_column_default(table_name, column_name, options[:default]) if options_include_default?(options)
        change_column_null(table_name, column_name, options[:null], options[:default]) if options.key?(:null)
      end