Random uniqueID for each ID SQL

Question

How can I improve this code? I wanted to know if there's a possibility to remove the for loop, and UPDATE a different uniqueID for each ID in my database.

<?php
 $reponse = $bdd->prepare("SELECT MAX(ID) FROM tuto WHERE title=''");
 $reponse->execute();
 $IDnow = $reponse->fetch(PDO::FETCH_ASSOC);
 $IDnow = $IDnow['MAX(ID)'];
 for ($i=2 ; $i <= $IDnow ; $i++){
 $reponse = $bdd->prepare("UPDATE tuto SET uniqueID=:uniqueID WHERE uniqueID='' AND title='' AND ID=:i");
 $uniqueID = $donnees['uniqueID'];
 $int = rand(0,51);
 $a_z = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
 $uniqueID = time().$a_z[$int];
 $reponse->execute([':uniqueID' => $uniqueID, 'i' => $i]);
 }
?>

• Bart Friederichs: This can be done in one SQL statement. Check out RAND()
• Used_By_Already: what sql dbms is it for? each vendor has a different approach, for example MySQL stackoverflow.com/questions/14798640/creating-a-rhttp://… MSsql stackoverflow.com/questions/1045138/… Oracle

Answer 1

Finally, I used RAND(), for generate an "UniqueID", and we can add some letters after or else :

Thanks to NerdyDev and Bart Friederichs for solutions.

<?php
$reponse = $bdd->prepare("UPDATE tuto SET uniqueID=ROUND(RAND() * :tp) WHERE uniqueID='' AND title=''");
$uniqueID = $donnees['uniqueID'];
$tp = time();
$reponse->execute([':tp' => $tp]);
?>

• Corbin: RAND() generates a float in [0, 1). This means it is incredibly likely to generate collisions once you're dealing with a non-small number of rows. Think about it this way: a float is 32 bits. That means you have around 4 billion unique values, but RAND() only uses from 0 to 1 (though there is actually a higher concentration of float values around 0 than far away from 0 -- but it's still relatively small).
• Dr.Blamo: In this example, :tp is the time, so RAND() * time. We can generates a lot of values, and we can add letters, etc...
• Corbin: I'll try to post an answer explaining why this is a flawed approach to generate collision-resistant IDs tomorrow, but for the time being, I've slapped together a simulation in C++ here. If you go to "Edit" then click "Ideone It" you can run it a couple of times. I've yet to see it take more than 10,000 ID generations to hit a collision. If these IDs just need to be likely-unique (~ 0.01% chance of collision), then this approach will work, but if you need an almost unimaginable chance of collision, then this is likely to cause you a lot of pain.
• Corbin: (It might be worth noting that the above simulation makes a few assumptions about MySQL's RAND(). Primarily, the MySQL manual does not specify whether RAND returns a 32 or 64 bit float, so I have assumed 32 bit. Also, I have assumed RAND is internally using Mersenne Twister and very rarely reseeding (two things I consider fair assumptions)).
• Dr.Blamo: Yes, I agree with you, but the collision is not important for a news UID, and we can put a condition to check If there are some collisions and regenerates by using RAND().

Answer 2

using foreach() loop will resolve your question.

<?php
$reponse = $bdd->prepare("SELECT MAX(ID) FROM tuto WHERE title=''");
$reponse->execute();
$IDnow = $reponse->fetch(PDO::FETCH_ASSOC);
$IDnow1 = $IDnow['MAX(ID)'];
foreach ($IDnow1 as $IDnow){
 $reponse = $bdd->prepare("UPDATE tuto SET uniqueID=:uniqueID WHERE uniqueID='' AND title='' AND ID=:i");
 $uniqueID = $donnees['uniqueID'];
 $int = rand(0,51);
 $a_z = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
 $uniqueID = time().$a_z[$int];
 $reponse->execute([':uniqueID' => $uniqueID, 'i' => $IDnow]);
 }
?>

let me know if still any issue stands with your question. Good Luck!

• Dr.Blamo: Not working, "Invalid argument", but I'll try foreach.
• NerdyDev: yes the foreach will resolve your problem for sure. and sorry i've might have not completed the code properly.