How i can execute a code every one minute in php?

How i can execute a code every one minute in php?

I wanna update my database when users visiting my site , every one minute,
I use this code :
$stmt = $dbConnection->prepare( "UPDATE db1_etchat_user SET alaghe=?
WHERE etchat_username=?");
$stmt->execute(array($alaghe,$username));
I wanna every one minute that's user visit my site , my columns be updated.
Excuse me for my bad English.