อยากรู้วิธีเช็ค validation ด้วย php อ่ะค่ะ ก่อนส่งค่าไปดาต้าเบส

<?php
// define variables and set to empty values
$nameErr = $emailErr = "";
$name = $email  = "";

if ($_SERVER["REQUEST_METHOD"] == "POST")
{
   if (empty($_POST["name"]))
     {$nameErr = "Name is required";}
   else
     {
     $name = test_input($_POST["name"]);
     // check if name only contains letters and whitespace
     if (!preg_match("/^[a-zA-Z ]*$/",$name))
       {
       $nameErr = "Only letters and white space allowed"; 
       }
     }
   
   if (empty($_POST["email"]))
     {$emailErr = "Email is required";}
   else
     {
     $email = test_input($_POST["email"]);
     // check if e-mail address syntax is valid
     if (!preg_match("/([\w\-]+\@[\w\-]+\.[\w\-]+)/",$email))
       {
       $emailErr = "Invalid email format"; 
       }
     }
     
}

function test_input($data)
{
     $data = trim($data);
     $data = stripslashes($data);
     $data = htmlspecialchars($data);
     return $data;
}
?>

<h2>PHP Form Validation Example</h2>
<p><span class="error">* required field.</span></p>
<form method="post" action="<?php $_SERVER["PHP_SELF"];?>"> 
   <label>Name:</label> <input type="text" name="name" value="<?php echo $name;?>"> <span class="error">* <?php echo $nameErr;?></span>
   <br><br>
   <label>E-mail:</label> <input type="text" name="email" value="<?php echo $email;?>"> <span class="error">* <?php echo $emailErr;?></span>
   <br><br>
  
   <input type="submit" name="submit" value="Submit"> 
</form>