php中mysql模块部分功能的简单封装

php中mysql模块部分功能的简单封装，很多cms都是封装了一些mysql的操作代码类，大家可以参考下。

代码如下:
class mysql
{
private $db; // datebase connect
private $result; // mysql result
static private $mysql; // mysql object
private function __construct()
{ // The work before Create an object
$this->db = mysql_connect('localhost','root','');
mysql_select_db('hello', $this->db );
}
public static function getObject()
{ //if have a object,return that object,Not create
if(! self::$mysql instanceof self)
self::$mysql = new self;
return self::$mysql;
}
public function query($sql)
{
$this->result = mysql_query($sql, $this->db);
return $this->result;
}
public function fetch()
{
if( isset($this->result ) )
return mysql_fetch_assoc( $this->result );
}
public function error()
{
return 'error:'.mysql_error();
}
public function num() // for sql select result
{
return mysql_num_rows( $this->result );
}
public function close()
{ // return true or false
return mysql_close( $this->db );
}
}

这样做看起来就只对可移植有用，其它的作用还体会不到