How to prevent form resubmission when page is refreshed (F5 / CTRL+R)

Question

I have a simple form that submits text to my SQL table. The problem is that after the user submits the text, they can refresh the page and the data gets submitted again with

Answer 1

You can prevent form resubmission via a session variable.

First you have to set rand() in a textbox and $_SESSION['rand'] on the form page:

  
 
   Your Form's Other Field 
 

After that check $_SESSION['rand'] with textbox $_POST['randcheck'] value like this:

if(isset($_POST['submitbtn']) && $_POST['randcheck']==$_SESSION['rand'])
{
    // Your code here
}