run query if explode is found

Please help, Im not sure how the result Im looking for is possible.

The query below will work ok, however it is possible that the url does not contain any trailing slashes after:
domain.com/index.php
This will run the query and all results from the field 'male' will be returned.

Is it possible to check and stop the query if no slashes are found or $first is not a valid letter??

list($first) = explode('/', substr($PATH_INFO,1));
$query = "SELECT DISTINCT `male`
FROM `model`
WHERE 1
AND `male` LIKE '$first%'";

$result = mysql_query($query);
$number = mysql_numrows($result);
{
for ($i=0; $i<$number; $i++) {
$male=mysql_result($result,$i,"male");

echo "$male";