public function addPrimary($column, $options = false) {
        $symbol = is_string($options) ? $options : '';

        if (empty($this->_primaryKey)) {
            $this->_primaryKey = [
                'constraint' => $symbol,
                'columns' => [$column]
            ];
        } else {
            $this->_primaryKey['columns'][] = $column;
        }

        return $this;
    }