PHP封装MySQL数据库连接

<?php
class db
{
	private $conn=null;
	public function __construct()
	{
		$this->conn = mysqli_connect('127.0.0.1','root','') or (mysqli_error());
		mysqli_select_db($this->conn,'samp');
		mysqli_query($this->conn,'set names utf8');
	}

	/*
	 *执行sql语句
	 *
	 */
	public function getResult($sql)
	{
		$result = mysqli_query($this->conn,$sql);
		$res = [];
		while(($row = mysqli_fetch_assoc($result))!=false){
			$res[] = $row;
		}
		return $res;
	}

	/*
	 *测试
	 */
	public function excise()
	{
		$sql = 'select * from user';
		return $this->getResult($sql);
	}
}
$db = new db();
$excise = $db->excise();
print_r($excise);