$mysql_server="localhost";
$mysql_username="数据库用户名";
$mysql_password="数据库密码";
$mysql_database="数据库名";
//建立数据库链接
$conn = mysql_connect($mysql_server,$mysql_username,$mysql_password) or die("数据库链接错误");
//选择某个数据库
mysql_select_db($mysql_database,$conn);
mysql_query("set names 'utf8'");
//执行MySQL语句
$result=mysql_query("SELECT id,name FROM 数据库表");
//提取数据
$row=mysql_fetch_row($result);

$db=new mysqli($dbhost,$username,$userpass,$dbdatabase);
if(mysqli_connect_error()){
echo 'Could not connect to database.';
exit;
}

$result=$db->query("SELECT id,name FROM user");
$row=$result->fetch_row();

$dsn='mysql:host='.$dbhost.';dbname='.$dbdatabase.';'
$dbh=new PDO($dsn,$username,$userpass);

$stmt=$dbh->query('SELECT id,name FROM user');
$row=$stmt->fetch();