สอบถามวิธีแก้ Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in D:\HOME\LOCALUSER\takbai\includes\class.mysql.php on line 171

<?
/*
	ชื่อไฟล์					class.mysql.php
	การใช้งาน				ใช้ในการเชื่อมต่อฐานข้อมูล MySQL
	ผู้เขียน					อัษฎา อินต๊ะ
	ติดต่อ					[email protected]
*/
if (eregi("class.mysql.php",$_SERVER['PHP_SELF'])) {
    Header("Location: ../index.php");
    die();
}

class DB{
	//ส่วนของการเชื่อมต่อ
	var $host = DB_HOST ;
	var $database ;
	var $connect_db ;
	var $selectdb ;
	var $db ;
	var $sql ;
	var $table ;
	var $where; 

	////////////////////// ฟังก์ชั่นต่างๆ //////////////////////
	//เชื่อมต่อดาต้าเบส
	function connectdb($db_name="database",$user="username",$pwd="password"){
		$this->database = $db_name;
		$this->username = $user;
		$this->password = $pwd;
		$this->connect_db = mysql_connect ( $this->host, $this->username, $this->password ) or sql_error ( "database-connect", mysql_error() );
		//$this->connect_db = mysql_pconnect ( $this->host, $this->username, $this->password ) or sql_error ( "database-connect", mysql_error() );
		$this->db = mysql_select_db ( $this->database, $this->connect_db) or sql_error ( "database-select", mysql_error() );
		mysql_query("SET NAMES TIS620"); 
		mysql_query("SET character_set_results=tis620"); 
		return true; 
	}

	//ปิดการเชื่อมต่อดาต้าเบส
	function closedb( ){
		mysql_close ( $this->connect_db ) or sql_error ( "database-close", mysql_error() );
	}

	//เพิ่มข้อมูล
	//$db->add_db("table",array("field"=>"value")); 
	function add_db($table="table", $data="data"){
		$key = array_keys($data); 
        $value = array_values($data); 
		$sumdata = count($key); 
		for ($i=0;$i<$sumdata;$i++) 
        { 
            if (empty($add)){ 
                $add="("; 
            }else{ 
                $add=$add.","; 
            } 
            if (empty($val)){ 
                $val="("; 
            }else{ 
                $val=$val.","; 
            } 
            $add=$add.$key[$i]; 
            $val=$val."'".$value[$i]."'"; 
        } 
        $add=$add.")"; 
        $val=$val.")"; 
        $sql="INSERT INTO ".$table." ".$add." VALUES ".$val; 
        if (mysql_query($sql)){ 
            return true; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
	}

	//แก้ไขข้อมูลแบบหลายฟิลล์ 
	//$db->update_db("tabel",array("field"=>"value"),"where"); 
    function update_db($table="table",$data="data",$where="where"){ 
        $key = array_keys($data); 
        $value = array_values($data); 
        $sumdata = count($key); 
        $set=""; 
        for ($i=0;$i<$sumdata;$i++) 
        { 
            if (!empty($set)){ 
                $set=$set.","; 
            } 
            $set=$set.$key[$i]."='".$value[$i]."'"; 
        } 
        $sql="UPDATE ".$table." SET ".$set." WHERE ".$where; 
        if (mysql_query($sql)){ 
            return true; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//แก้ไขข้อมูลแบบฟิลล์เดียว
	//$db->update("table","set","where");
	function update($table="table",$set="set",$where="where"){ 
        $sql="UPDATE ".$table." SET ".$set." WHERE ".$where; 
        if (mysql_query($sql)){ 
            return true; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//ลบข้อมูล
	//$db->del("table","where"); 
    function del($table="table",$where="where"){ 
        $sql="DELETE FROM ".$table." WHERE ".$where; 
        if (mysql_query($sql)){ 
            return true; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//นับจำนวนแถวข้อมูล
	//$db->num_rows("table","field","where"); 
    function num_rows($table="table",$field="field",$where="where") { 
        if ($where=="") { 
            $where = ""; 
        } else { 
            $where = " WHERE ".$where; 
        } 
        $sql = "SELECT ".$field." FROM ".$table.$where; 
        if($res = mysql_query($sql)){ 
            return mysql_num_rows($res); 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//Query ข้อมูล
	//$res = $db->select_query('SELECT field FROM table WHERE where'); 
    function select_query($sql="sql"){ 
        if ($res = mysql_query($sql)){ 
            return $res; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//นับจำนวนแถวข้อมูล
	//$res = $db->select_query('SELECT field FROM table WHERE where'); 
	//$rows = $db->rows($res); 
    function rows($sql="sql"){ 
      if ($res = mysql_num_rows($sql)){ 
            return $res; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

	//ดึงค่า array
	/*$res = $db->select_query('SELECT field FROM table WHERE where'); 
     while ($arr = $db->fetch($res)) { 
			echo $arr['a']." - ".$arr['c']."<br>\n"; 
	}*/

// function เดิม

   function fetch($sql="sql"){ 
      if ($res = mysql_fetch_assoc($sql)){ 
            return $res; 
        }else{ 
            $this->_error(); 
            return false; 
        } 
    } 

//แสดงข้อความผิดพลาด
    function _error(){ 
        $this->error[]=mysql_errno(); 
    } 

}
?>