modifyColumn example

$sqlTable = new Table($this->db, $this);

                $sqlTable->fromTable($table)
                    ->dropColumn($field)
                    ->run();

                return '';

            case 'CHANGE':
                (new Table($this->db, $this))
                    ->fromTable($table)
                    ->modifyColumn($field)
                    ->run();

                return null;

            default:
                return parent::_alterTable($alterType, $table, $field);
        }
    }

    /** * Process column */