code: def change_column(table_name, column_name, type, options = {}) #:nodoc:
        change_column_sql = "ALTER TABLE #{quote_table_name(table_name)} " <<
            "ADD #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit])}"
        add_column_options!(change_column_sql, options)
        execute(change_column_sql)
      end
docs: + change_column
   This only works in a VERY limited fashion.  For example, VARCHAR columns
   cannot be shortened, one column type cannot be converted to another.