PHP error Warning:mysql_query() solution, warningmysql_query_PHP tutorial

PHP error Warning: mysql_query() solution, warningmysql_query

php prompt error: Warning: mysql_query() [function. mysql-query]: Access denied for user 'ODBC'@'localhost' (using password: NO)
Code:

<&#63;php 
class mysqlClass 
{ 
function mysqlClass($host='localhost',$user='root',$pw='',$db='mysql') 
{ 
$this->link=mysql_connect($host,$user,$pw); 
mysql_select_db($db); 
} 
function query($sql){ 
mysql_query($sql); 
} 
function __destruct(){ 
mysql_close($this->link); //multi construct will cause error 
} 
// liehuo,net 
} 
$db=new mysqlClass(); 
$db=new mysqlClass(); 
$db->query("select * from user"); 

Reason:
When mysqlClass is initialized for the second time, mysqlClass is initialized first and the same $this->link as the first $db is obtained. Then calling the __construct function will close this->link.
Finally, the mysql resource in $db is empty and an error pops up.
Solution:
$db=$db?$db:new mysqlClass();
or
$this->link=mysql_connect($host,$user,$pw,true);

I hope the solutions provided can really help everyone.