PHP 连接数据库的3种方式

$mysql_server='localhost';
$mysql_username='用户名';
$mysql_password='用户密码';
$mysql_database='数据库名';//建立数据库连接
$conn=mysql_connect($mysql_server,$mysql_username,$mysql_password) or die('数据库连接失败！');//选择某个数据库
mysql_select_db($database,$conn);
mysql_query("set names 'utf8'");//执行sql语句
$result=mysql_query(select * from database where id=1);//提取数据
$row=mysql_fetch_row($result);

$db=new mysqli($dbhost,$username,$password,$database);
if(mysqli_connect_error()){  
  echo '连接错误';    
  exit;
}$result=$db->query("select * from database where id=1");
$row=$result->fetch_array();

    $db=new pdo('mysql:dbname=cms;host=127.0.0.1','php','password');
        $result=$db->query("select * from database where id=1");
            $row=$result->fetchAll();