php开启mysqli扩展之后如何连接数据库

<?php
$connect = mysqli_connect('localhost','root','','volunteer') or die('Unale to connect');
$sql = "select from vol_msg";
$result = mysqli_query($connect,$sql);
while($row = mysqli_fetch_row($result)){
echo $row[0];
}
?>

<?php
//创建对象并打开连接，一个参数是选择的数据库名称
$mysqli = new mysqli('localhost','root','','volunteer');
//检查连接是否成功
if (mysqli_connect_errno()){
//注意mysqli_connect_error()新特性
die('Unable to connect!'). mysqli_connect_error();
}
$sql = "select from vol_msg";
//执行sql语句，完全面向对象的
$result = $mysqli->query($sql);
while($row = $result->fetch_array()){
echo $row[0];
}
?>