Random dosieid number that is not used - php

Question

I'm trying to generate a unique "dosieid" number for my web site. My web site is a human resources program solution, in that program users create dosie of their workers in their firm ...random dosieid needs me so when user creating dosie in field dosieid automatically show the dosieid-s that are not used before...the dosieid that don't exist in database. In other case I would use auto increment but in this case dosie is not created yet. And in form dosieid must be option to change the number if random is not fine with a user. One more hint the numbers must bee from 1 to 9999. Can someone help me? I have try many codes but I have not find something like one with this spec.
This is what I have do so far. It gets the random number but I don't know how to compare that random number with database row "dosieid" ?
$id_num = mt_rand(1,9999);
$query = "SELECT dosjeid FROM albums";
$result = mysql_query($query) or die(mysql_error());
while($account = mysql_fetch_array($result)){
if ($id_num == $account['id']){
$id_num = mt_rand(1,9999);
}
}
echo"$id_num<br>";

Answer 1

This is extraordinarily convoluted... why is an auto-incrementing number not enough? This code would also never work properly. If for whatever reason you HAVE to use a random number, then you'd do it like this:
while(true) {
$id_rand = mt_rand(1,9999);
$result = mysql_query("SELECT count(*) FROM albums WHERE dosjeid=$id_rand") or die(mysql_error());
$row = mysql_fetch_row($result);
if ($row[0] == 0) {
break; // our random number isn't in the database, so exit the loop
}
}
However, here's some problems with this:
1) You'll get an infinite loop when you reach 9999 dosie records
2) The more records there are in the database, the longer this loop will take to find a "vacant" slot. As you get closer and closer to 9999 records, you'll be taking a LONG time to find that one empty slot
3) If you're trying to "cloak" the IDs of anyone member so that users can't simply increment an ID parameter somewhere to see other people's records, there's FAR FAR FAR better/easier ways of doing this, such as encrypting the ID value before sending it out to clients.

Answer 2

Use a auto-increment number as your primary key and an additional display id with the UNIQUE attribute as the ID shown to the user. This way you have a unique ID for your internal processing and a display ID that can be easily changed.

Answer 3

This is a terrible design. You should either:
not let users create the dosieid (create it yourself, give it to them after record created)
Try to create a stub record first with an assigned dosieid, and then update it with information
or use UUIDs, which requires a much bigger range than 1-9999
Even if you check that the number was unique, in between the time when you check it and the time you insert the record someone else may have taken it.
And under no circumstances should you find an empty id by picking numbers at random. This makes your program execution time non-deterministic, and if you eventually get 5000 employees you could be waiting a long time.
Also, This range is way too small for a randomness requirement.

Answer 4

You may also want to read about number only hashes (check upon the algorithm's collision rate) - php: number only hash?
function doesIdExists($id)
{
$query = "SELECT dosjeid FROM albums";
$result = mysql_query($query) or die(mysql_error());
while($account = mysql_fetch_array($result))
{
if ($id_num == $account['id'])
return true; /* The id is taken */
}
return false; /* Not taken */
}
$recNotAdded = true;
while($recNotAdded)
{
$rand = mt_rand(1,1000); //Whatever your numbers
$doesExist = doesIdExists($rand);
if(!$doesExist)
{
/* Add to DB */
$recNotAdded = false;
}
}