PHP数据库连接

<?php
$host="localhost";
$username="root";
$password="123456";
$dbname="PHP";
$connID=mysqli_connect($host,$username,$password);
if (mysqli_select_db($connID,$dbname)) {
    echo "数据库连接成功";
}
else
{
    echo "数据库连接失败";
}


?>

<?php
define('host','localhost');
define('user','root');//数据库用户名 root
define('pwd','123456');//数据库密码
define('db','PHP');//数据库名
$conn = new mysqli(host,user,pwd,db);
if ($conn->connect_error){
    die("连接失败：".$conn->connect_error);
}else{
    echo "连接成功";
}