Php 谁能解释一下我哪里做错了什么？

当我运行这段代码时，它显示解析错误。有人能帮我吗

 $servername = "localhost";    
$username = "root";      
$password = "";      
$dbname = "form";    

 // Create connection      
$conn = new mysqli($servername, $username,$password, $dbname);          
// Check connection      
if ($conn->connect_error) {
     die("Connection failed: " .$conn->connect_error);      
}  
 SELECT * FROM my_db;    
 $conn->close();

---

您应该使用php标记并删除那些“>”，还应该使用mysqli_query从mysql查询数据

<?php
$servername = "localhost";    
$username = "root";      
$password = "";      
$dbname = "form";    

 // Create connection      
$conn = new mysqli($servername, $username,$password, $dbname);          
// Check connection      
if ($conn->connect_error) {
    die("Connection failed: " .$conn->connect_error);      
}  
$query = mysqli_query($conn,"SELECT * FROM my_db");    
$conn->close();
?>

可能都是那些“>”符号。您是否试图在php脚本中运行SQL命令？所有那些标志都不起作用。我收到这个警告：mysqli_query（）至少需要2个参数，1个参数在第13行的C:\xampp\htdocs\prajwol\php\try.php中给出