You can do this quite easily - either server or client side. If you want to do it client side you need to right a simple javascript to validate your search form. There are loads of sample "javascript validation" scripts around if you search on google or your favorite javascript resource.
The other simple way to do this is by checking for the values of your search fields before doing the search. So in the page the search form points to, just check with somethings like this -
if ($_POST['searchField1'] || $_POST['searchField2'] || $_POST['searchField3']) {
do_search();
}
else {
tell_em_where_2_go();
}
Hope this helps 😉
