Prevent user to use back button with warning or disable any insert

Question

I have a form in page1.php which directs to page2.php from where the data from the form in page1.php is inserted into database. after

Answer 1

Instead of giving link to a third page, redirect to the very same URI
this is quite handy method called POST/Redirect/GET:
here is a concise example of it:

 $val) {
      $form[$key] = htmlspecialchars($val);
    }
  }
} else {
  $form['name'] = $form['comments'] = '';  
}
include 'form.tpl.php';
?>  

Here you can see another example, concise yet powerful: Separating Logic/Style in PHP properly
it's complete solution to display, add and edit database contents, exactly for admin purpose.