Column type cannot be auto-increment for small int types

switch type {

    case self::TYPE_INTEGER:
    case self::TYPE_BIGINTEGER:
            let this->_autoIncrement = true;
            break;

    default:
            throw new Exception("Column type cannot be auto-increment");
}

Why we can't use smaller integer types as AI?

well it's right, we should add tinyint, smallint and medimumint. Create an issue in github

Good luck