Simple inserting data to DB with basic PHP.

simple_insert.php

<?php


if(isset($_POST['submit']))
{
  $firstName = $_POST['firstName'];
  $lastName = $_POST['lastName'];
  $email = $_POST['email'];
  $subject= $_POST['subject'];
  $message = $_POST['message'];
	
  $sql="INSERT INTO sentmessage(firstName, lastName, email, subject, message)VALUES('$firstName','$lastName','$email', '$subject','$message')";
  $sql_check = mysqli_query($link, $sql) or die("Query failed");

	if($sql_check) 
	{
			echo ("<SCRIPT LANGUAGE='JavaScript'>
			window.alert('Thank You for Your Message!');
			window.location.href='contact.php'
			</SCRIPT>"); 
			exit();
	}
	else 
	{
				echo ("<SCRIPT LANGUAGE='JavaScript'>
				window.alert('Error!');
				window.location.href='contact.php'
				</SCRIPT>"); 
	}
}
?>