How to get current page's isset - php

Question

Firstly, I havent been able to find anything useful on the subject, anywhere really.
I'm trying to make something somewhat simular to a forum,
A small explanation,
(And yes, I know its not seo, but I'm only looking for functionality atm.)
Lets say you go to example.com/?1, Then the database entry with the ID of 1 would be displayed on the index page, If you go to example.com/?3 then the DB entry with the ID of 3 would be displayed, etc..
DB Structure
----------------------------------------
| id | label | description | parent_id |
|---------------------------------------
| 1 | General | NULL | 0 |
| 2 | Public | NULL | 1 |
| 3 | Private | NULL | 1 |
----------------------------------------
PHP Code
if ($stmt = $mysqli->prepare("SELECT id, label, description, parent_id FROM categories")) {
$stmt->execute(); // Execute the query.
$stmt->store_result();
$stmt->bind_result($id, $label, $desc, $parent); // Get variables from result.
while ($stmt->fetch()) {
if(isset($id)) {
echo "Hello, This is the $label category";
}
}
}
What i'm missing is a way to get the users current "isset" (.com/?10, .com/?5, ETC) Before the query is run so i can check for that isset in the DB and get the correct values, right now it's outputting all rows in the DB, I would highly appreciate any help with it :)
If you know of a better way of doing something like this(without using a framework), please let me know!

Answer 1

From a terminology standpoint, it sounds like you are interested in understand what parameters are passed in the request's query string.
In your case, you are doing something a little weird in that be having URI format like /?* where * is integer ID value, you would actually be passing a variably named parameter. Since you don't know what the parameter name is, you would have to do something like
$ids_in_query_string = array_keys($_GET);
To store the key names which infer which ID(s) were requested.
What I would suggest is to form your query string like /?id=*, that way you always know which key in $_GET to check against. For example:
$id = null;
if (!empty($_GET['id']) && is_numeric($_GET['id'])) {
$id = $_GET['id'];
}
if (!is_null($id)) {
// perform your query for selected ID
} else {
// do something else
}