mysql_fetch_assoc and extract

Using extract after using mysql_fetch_assoc is handy for variables, but if no row if returned, you've got a problem. First you get an error on the extract needing an array, then you've got the same variables from the previous loop. It would be very handy if extract could do a complete prefix unset first. For example, if my prefix were "my", it would unset every last variable starting with $my_ . And it would also not return an error on empty. Or if that's asking for too much, having a wildcard unset would be awesome ... unset($my_*). Anyone have a special function doing just that? Thanks.