php - Old database connection class with functions deprecated

Working on an old website (PHP 3), I need to update its code, notably this DB connection class (mysql_db_query seems deprecated) :

class db {

var $host; 
var $port;
var $login;
var $pass;
var $data_base;

function db(){
    $this->host = "";
    $this->port = ""; 
    $this->login = "";

    $this->pass = "";
    $this->data_base = "";
}

function connect() {
    return mysql_connect($this->host.':'.$this->port, $this->login, $this->pass);
}

function query( $query ){
    if ( $query )

        return mysql_db_query($this->data_base,$query);
        return mysql_query($query);
    return 0;
}

function close( $link ){
    mysql_close($link);
}
}

Could anyone tell me how to update it?

Thank you by advance for your help.