PHP PDO Unique Random Number Generator - php

Question

Hello so first of all please consider this question as a newbie one because I can just set an ID field and add zerofill so it would look like 000001, 000002 and so fort. But what I did is wrong, and the system is already big so please consider my question. I have a table named accounts which has an id field and sponsorID field. Now what I did looks like this (btw I am using slim framework):
$db = new db();
$sponsorIDrandom = mt_rand(100000, 999999);
$bindCheck = array(
":sponsorID" => $sponsorIDrandom
);
$sponsorIDChecker = $db->select("accounts", "sponsorID = :sponsorID", $bindCheck);
$generate_SID = null;
do {
$generate_SID = mt_rand(100000, 999999);
} while (in_array($generate_SID, array_column($sponsorIDChecker, 'sponsorID')));
$db->insert("accounts", array(
"sponsorID" => $generate_SID
));
The code above will check if a number already exist in the accounts table and if there is an existing, it will generate a random number again until it becomes unique or non-existing in the accounts table. I made the sponsorID field unique so that it won't accept duplicate values.
Now the problem is the code I posted. I thought it would let the $generate_SID be unique because I used the in_array function so it would check if a value already exist in the array and do generate a number again until it is unique but I did receive luckily an error that it tried to insert a random number that already exists and it didn't generate a new one.
Can anyone tell me if there's a solution for this? Or should I re-modify the code above so it would not enter already existing sponsorID? Thank you in advance.

Answer 1

From what i understood, you try to insert a unique id into a table but the generator only runs once and or it tells you that the number already exists.
I've never used slim but it seems in your code you try to do a SELECT of a single record, because you generate a random number and then ask for this number to the database:
$sponsorIDrandom = mt_rand(100000, 999999);
$bindCheck = array(
":sponsorID" => $sponsorIDrandom
);
$sponsorIDChecker = $db->select("accounts", "sponsorID = :sponsorID", $bindCheck);
This only returns one or none rows if as you say the sponsorID is UNIQUE.
And then you try to generate another random number and check if is not repeated based on this single (or null) record.
$generate_SID = null;
do {
$generate_SID = mt_rand(100000, 999999);
} while (in_array($generate_SID, array_column($sponsorIDChecker, 'sponsorID')));
this loop only executes once because the probability of this second random number to be inside this record (if there is a record at all) are almost none and if the database are as big as you says, then the probability for collisions are too high.
for this code to work you need to load every record or ask for the newly generated number if it exists in the database every time it is generated, both alternatives are not recommended but since the databse is already (almost) full.
$sponsorIDChecker = $db->select(...); //use the equivalent of "SELECT sponsorID from accounts" without the WHERE clause, is better to ask for a single column.
$generate_SID = null;
do {
$generate_SID = mt_rand(100000, 999999);
} while (in_array($generate_SID, ...)); //here you put the result of the query above.
$db->insert("accounts", array(
"sponsorID" => $generate_SID
));
Now, something that may be of help: if you set the sponsorID as a zerofill in the databse as you said
I can just set an ID field and add zerofill so it would look like 000001, 000002 and so fort.
then you can lower the min value of mt_rand to 0 and you gain 100000 more IDs to try.