//选择数据库
 function select($db = "")
 {
  if(!$this->db_link)
  {
   if($this->debug){$this->debuginfo .= "没有可用的数据库连接！\r\n";}
   $this->db_ready = false;
  }
  if("" == $db)
  {
   if(mysql_select_db($this->db_name))
    $this->db_ready = true;
  }
  if(mysql_select_db($this->db_name = $db))
   $this->db_ready = true;
  return $this->db_ready;
 }

 //执行查询
 function execute($SQL = "")
 {
  if("" != $SQL)
  {
   $this->db_query_sql = $SQL;
   //if($this->debug){$this->debuginfo .= "SQL is null!\r\n";}
   //return false;
  }
  if("" == $this->db_query_sql)
  {
   if($this->debug){$this->debuginfo .= "SQL is null!\r\n";}
   return false;
  }
  $this->db_recordset = mysql_query($this->db_query_sql);
  return true;
 }
}

$dbmy = new DBCLS(); //创建一个DBCLS对象
if(!$dbmy->connection_string("Server=localhost;DataBase=mysql;UserID=root;PassWord=123456"))//初始化DBCLS对象dbmy

print $dbmy->debuginfo; //初始化失败，输出错误信息

else

print $dbmy->connection_string(); //初始化成功，输出连接字符串
print "\r\n";

if(!($dbmy->connect()) or !($dbmy->select())) //如果连接数据库，或者选择数据库失败
print $dbmy->debuginfo;                               //输出出错信息
//$dbmy->db_query_sql = "select * from user";
if($dbmy->execute())              //执行查询指令
{                                 //如果不出错
 var_dump($dbmy->db_recordset);//输出返回的结果集
}
?>

输出信息：

---------- php debug ----------
Server=localhost;DataBase=mysql;UserID=root;PassWord=123456
resource(5) of type (mysql result)

Output completed (1 sec consumed) - Normal Termination