PHP check if ID already is in use - php

Question

I am currently busy with creating my own 6 player game based on PHP/MySQL. I want to check if the ID from players_online is already in use, if yes then it need to keep searching until it found one (till max 6) else it need to return 0;
$con is the connection to the database and you can find the settings on the .mysql_config.php
This is what I got:
function find_local_id()
{
include'./mysql_config.php';
$i=1;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
$i++;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
$i++;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
$i++;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
$i++;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
$i++;
$select_id=mysqli_fetch_assoc(mysqli_query($con, "SELECT `ID` FROM `players_online` WHERE ID = ".$i.""));
if ($select_id["ID"] == $i) {
return 0;
} else {
return 6;
}
} else {
return 5;
}
} else {
return 4;
}
} else {
return 3;
}
} else {
return 2;
}
} else {
return 1;
}
Is there a way to have this smaller/compact? Because I think this is pretty big for just a small function. :)

Answer 1

I think this would work:
function find_local_id()
{
include'./mysql_config.php';
$result = mysqli_query($con, "SELECT `ID` FROM `players_online`");
while($row = mysqli_fetch_assoc($result)) {
$ids[] = $row['ID'];
}
if($available = array_diff(range(0, 6), $ids)) {
return min($available);
}
return 0;
}
If you have mysqli_fetch_all use that.
Get all of the IDs in the table
See which ones (1-6) are not in the results
If any are available return the lowest one
If not return 0

Answer 2

First of all, you could use a loop to do this (but you don't need one).
You're hitting the DB many times unnecessarily.
Create a function or query (like the one below) that accepts one integer id and returns the count of rows.
<?php
$db = new PDO('mysql:host=localhost;dbname=yourdb', 'user', 'pass');
$id = ''; //input, whether it be a param from a function, session superglobal, GET or POST.
$exists = $db->prepare('SELECT id FROM players_online WHERE id = ?');
$exists->execute(array($id));
echo $exists->rowCount(); // if greater than 1 or equal, it exists.

Answer 3

You'd be far better off doing something like
$sql = "SELECT * FROM players_online WHERE id BETWEEN {$i} AND {$i}+6";
$stmt = mysqli_query($con, $sql) or die(mysqli_error($con));
$in_use = mysqli_num_rows($stmt);
If all 6 IDs are in the database, then you'll get 6 rows in $in_use. If 5 show up, then you'll get 5 rows, etc...

Answer 4

You seem to have a really flawed design in that you are never going to scale for more than one game at at time with this approach, are going to need to delete rows from your table to make it work when generating a new game, and are going to have problems with race conditions in cases where concurrency is high. But assuming you have a means for managing inserting player record id's in order (1,2,3, etc.). Your query can simply be:
SELECT MAX(id) FROM players_online
This will tell you the current highest id in the table. You would simply insert the next player with the id value incremented by 1 above the current max value.