为什么mysqli_query($conn,$sql)or die(mysqli?报错

<?php
ini_set("error_reporting",E_ALL ^ E_NOTICE);
class T3 {
	
	private $ser;
	private $usr;
	private $psw;
	private $dbn;
	private $conn;
	
	private $id;
	private $label;
	private $author;
	private $content;
	private $date;
	private $sql;
	
	function __construct($ser,$usr,$psw,$dbn){
		$this->ser = $ser;
		$this->usr = $usr;
		$this->psw = $psw;
		$this->dbn = $dbn;
		$this->connection();
		
	}
	
	function connection(){
		$conn = mysqli_connect($ser,$usr,$psw,$dbn);
		mysqli_query($conn,"set names 'GBK'");
		echo "connected";
	}
	
	function query(){
		$sql ="select * from t";
		$result = mysqli_query($conn,$sql)or die(mysqli_errno());
		$row = mysqli_fetch_array($result);
		while ($row){
			echo $row['id'].'<br>';
		}
	}
	
}

$t = new T3("localhost","root","","test");
$t->query();
?>

请问为什么总是报错，希望大神能指出错误和修正，谢谢，本人小白