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

After inserting it to database, call unset() method to clear the data.

unset($_POST);

To prevent refresh data insertion, do a page redirection to same page or different page after record insert.

header('Location:'.$_SERVER['PHP_SELF']);