php7如何连接数据库

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

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

 ?>

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

 ?>

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

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('select * from customers');
	$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 $error){
	echo 'connect failed:'.$error->getMessage();
}

 ?>