code: protected function appendPart($part, $sql, $bind = false) 
  	{
  		if (!is_array($sql)) $sql = [$sql];
  		
  		if (!$this->parts[$part]) 
  		{
  			$this->parts[$part] = $sql;
  		}
  		else
  		{
  			$this->parts[$part] = array_merge($this->parts[$part], $sql);
  		}
  		
  		return $this->appendBind($part, $bind);
  	}
docs: Append new query to given part.
  @param int $part Part to append to.
  @param string $sql Command to append.
  @param array|bool $bind Bind params.
  @return static