PHP7 はどのようにしてデータベースに接続できますか

<?php
$serve = &#39;localhost:3306&#39;;
$username = &#39;root&#39;;
$password = &#39;admin123&#39;;
$dbname = &#39;examples&#39;;
$mysqli = new Mysqli($serve,$username,$password,$dbname);
if($mysqli->connect_error){
	die(&#39;connect error:&#39;.$mysqli->connect_errno);
}
$mysqli->set_charset(&#39;UTF-8&#39;); // 设置数据库字符集

$result = $mysqli->query(&#39;select * from customers&#39;);
$data = $result->fetch_all(); // 从结果集中获取所有数据
print_r($data);

 ?>

<?php
$serve = &#39;localhost:3306&#39;;
$username = &#39;root&#39;;
$password = &#39;admin123&#39;;
$dbname = &#39;examples&#39;;
$link = mysqli_connect($serve,$username,$password,$dbname);
mysqli_set_charset($link,&#39;UTF-8&#39;); // 设置数据库字符集
$result = mysqli_query($link,&#39;select * from customers&#39;);
$data = mysqli_fetch_all($result); // 从结果集中获取所有数据
print_r($data);

 ?>

<?php
$serve = &#39;mysql:host=localhost:3306;dbname=examples;charset=utf8&#39;;
$username = &#39;root&#39;;
$password = &#39;admin123&#39;;

try{ // PDO连接数据库若错误则会抛出一个PDOException异常
	$PDO = new PDO($serve,$username,$password);
	$result = $PDO->query(&#39;select * from customers&#39;);
	$data = $result->fetchAll(PDO::FETCH_ASSOC); // PDO::FETCH_ASSOC表示将对应结果集中的每一行作为一个由列名索引的数组返回
	print_r($data);
} catch (PDOException $error){
	echo &#39;connect failed:&#39;.$error->getMessage();
}

 ?>