protected function setKey(Field & $field, $key, $extra)
    {
        $key = strtoupper($key);

        if ($key == 'PRIMARY KEY') {
            $field->isPrimary = true;
        }

        if ($key == 'MUL') {
            $field->isIndex = true;
        }

        if ($key == 'UNI') {
            $field->isUnique = true;
        }

        if (strtolower($extra) == 'auto_increment') {
            $field->isAutoIncrement = true;
        }

        return $this;
    }