Conditional object.

MySQL question:
Hi,
when I do:
...
$sth = $db->prepare("select nome from empresas where (uf = '$unif' and prod_serv like '%$field%')");

while (@array = $sth->fetchrow_array) {
($var) = @array;

if ($var eq "") {
$firma = "javascript URL_s()";
}
else {
$firma = "dyn_a.cgi?unif=$unfed&p_s=$field&p_s1=$var";
}
}

print "$firma;"
exit;

Question:

If $var has date $firma return Ok.
If $var has no date $firma return empty (???).

Thanks.