这个PHP类是否针对mysql数据库访问进行了优化?

从性能的角度来看,我知道每次执行查询时都打开与数据库的连接可能不是一个很好的做法(而且当我尝试使用mysql_real_escape_string()过滤输入时,它不起作用,因为没有活动的数据库连接)。但我想进一步澄清这一点。这样做很不对吗?为什么?我还想知道一些好的替代方案。

class DB {

private $conn;

//database data
private $dbhost;
private $dbname;
private $dbuser;
private $dbpass;

/**
 * Constructor
 * @dbhost string the database host
 * @dbname string the database name
 * @dbuser string the database username
 * @dbpass string the database password
 */
public function __construct ($dbhost, $dbname, $dbuser, $dbpass)
{
    $this->dbhost = $dbhost;
    $this->dbname = $dbname;
    $this->dbuser = $dbuser;
    $this->dbpass = $dbpass;
}

/**
 * Connects to mysql database
 */
private function open ()
{
    $this->conn = mysql_connect ($this->dbhost, $this->dbuser, $this->dbpass)
    or die ("Error connecting to database");

    mysql_select_db ($this->dbname) or die ("Error selecting database");
}

/**
 * Closes the connection to a database
 */
private function close ()
{
    mysql_close($this->conn);
}

/**
 * Executes a given query string
 * @param string $query the query to execute
 * @return mixed the result object on success, False otherwise
 */
public function query ($query)
{   
    $this->open();
    $result = mysql_query($query, $this->conn)
    or die ("Error executing query ".$query." ".mysql_error());

    $this->close();
    return $result;

}

}