code: public function compile()
  	{
  		$sql = array("INSERT INTO");
  		$sql[] = $this->table;
  		$sql[] = "(".join(', ', $this->columns).")";
  		$sql[] = "VALUES";
  
  		$values = array();
  		foreach ($this->values as $row)
  		{
  			$placeholders = array_fill(0, count($row), "?");
  			$values[] = "(".join(", ", $placeholders).")";
  			$this->params = array_merge($this->params, $row);
  		}
  
  		$sql[] = join(', ', $values);
  
  		return join(' ', $sql);
  	}
docs: Compiles the query into raw SQL
  
  @return  string