function select($fields,$filter=NULL,array $options=NULL,$ttl=0) {
		list($sql,$args)=$this->stringify($fields,$filter,$options);
		$result=$this->db->exec($sql,$args,$ttl);
		$out=[];
		foreach ($result as &$row) {
			foreach ($row as $field=>&$val) {
				if (array_key_exists($field,$this->fields)) {
					if (!is_null($val) || !$this->fields[$field]['nullable'])
						$val=$this->db->value(
							$this->fields[$field]['pdo_type'],$val);
				}
				unset($val);
			}
			$out[]=$this->factory($row);
			unset($row);
		}
		return $out;
	}