php中连接myql数据库的两种方式

<?php
$host=&#39;localhost&#39;;
$dbname=&#39;grade&#39;;
$username=&#39;root&#39;;
$password=&#39;root123456&#39;;

$pdo=new PDO("mysql:host=$host;dbname=$dbname",$username,$password);

echo "连接成功"."<br>";
?>

<?php
$servername="localhost";
$username="root";
$password="root123456";
$dbname="grade";
$link = mysqli_connect($servername, $username, $password, $dbname);

if (mysqli_connect_errno()) {
    printf("连接失败: %s\n", mysqli_connect_error());
    exit();
}
echo "连接成功"."<br>";