public function getExpressionData()
    {
        $data = parent::getExpressionData();
        
        if ($this->default !== null) {
            $data[0][0]  .= ' DEFAULT %s';
            $data[0][1][] = $this->default;
            $data[0][2][] = self::TYPE_VALUE;
        }
        
        return $data;
    }