private function sqlForUpdate()
 {
     $sql = 'ALTER TABLE `' . $this->tableName() . '` ';
     foreach ($this->fields() as $field) {
         // See if there are any parameters to pass to the field
         if (property_exists($field, 'params')) {
             $params = $field->params;
         } else {
             $params = FALSE;
         }
         $field = new Field($field->name, $field->type, $params);
         foreach ($field->sqlForColumns() as $column) {
             $sql .= 'ADD COLUMN ' . $column . ', ';
         }
     }
     return substr($sql, 0, -2) . ';';
 }