recursive function for getting parent and child

function categoryChild($id) {
$s = “SELECT ID FROM PLD_CATEGORY WHERE PARENT_ID = $id”;
$r = mysql_query($s);
$children = array();
if(mysql_num_rows($r) > 0) {
# It has children, let’s get them.
while($row = mysql_fetch_array($r)) {
# Add the child to the list of children, and get its subchildren
$children[$row['ID']] = categoryChild($row['ID']);
}
}
return $children;
}