php alphanumeric id with fixed letter position

Question

I need to create unique alphanumeric IDs, 6 characters long in PHP.

Although I have found a lot of answers solving this problem, I would like the letters to be positioned in specific place in the ID, for example A1B2C3 (first, third and fifth character).

My only solution for this is to create 6 "for" loops (a-z and 0-9 * 3 times) and insert the output in an array and then in MySQL table. There will definitely be no duplicates but is there any better way?

My code so far is:

<?php

   $id=array();

   for($a='A';$a!='AA';$a++){
        for($b=1;$b<=9;$b++){
           for($c='A';$c!='AA';$c++){
              for($d=1;$d<=9;$d++){
                  for($e='A';$e!='AA';$e++){
                     for($f=1;$f<=9;$f++){

                       $id[]=$a.$b.$c.$d.$e.$f;
                     }
                  } 
              }
           }
        }
    }

    foreach ($id as $value) {
        echo "$value \n";
    }
?> 

Answer 1

If you need sequential IDs:

// to start
//$numIds = 20000;
//$id = '';

// to add more
$numIds = 1000;
$id = 'A1J5M2'; // put MAX id from DB here

if ( '' !== $id ) { // increment id
  list($aa, $bb, $cc, $dd, $ee, $ff) = str_split($id);
  $arr = [$aa, $bb, $cc, $dd, $ee, $ff];
  list($aa, $bb, $cc, $dd, $ee, $ff) = incc($arr, count($arr) - 1);
}
else {
  list($aa, $bb, $cc, $dd, $ee, $ff) = ['A',1,'A',1,'A',1];
}

// generate ids    
$ids = [];

for($a=$aa;$a!='AA';$a++){
  for($b=$bb;$b<=9;$b++){
    $bb = 1; // reseting b - f is necessary when adding more ids
    for($c=$cc;$c!='AA';$c++){
      $cc = 'A';
      for($d=$dd;$d<=9;$d++){
        $dd = 1;
        for($e=$ee;$e!='AA';$e++){
          $ee = 'A';
          for($f=$ff;$f<=9;$f++){
            $ff = 1;

            $ids[] = "$a$b$c$d$e$f";
            // break out of all loops when desired number is reached
            if ( $numIds <= count($ids) ) { break 6; }
}}}}}}

// db setup
$conn = mysqli_connect('localhost', 'root', '', 'dbtest');
$insertstmt = mysqli_prepare($conn, 'INSERT INTO ids (id) VALUES (?)');

// insert ids
mysqli_stmt_bind_param($insertstmt, 's', $id);    
mysqli_autocommit($conn, false);
foreach ( $ids as $id ) {
  mysqli_stmt_execute($insertstmt);
}
mysqli_commit($conn);
mysqli_close($conn);


// function to increment given id, accommodates rolling over, e.g., A9 -> B1
function incc ($arr, $idx) {
  if ( is_int(intval($arr[$idx])) ) {
    if ( 9 == $arr[$idx] ) {
      $arr[$idx] = 1;
      $arr = incc($arr, --$idx); // recursing
    }
    else {
      $arr[$idx]++;
    }
  }
  else {
    if ( 'Z' === $arr[$idx] ) {
      $arr[$idx] = 'A';
      $arr = incc($arr, --$idx);
    }
    else {
      $ord = ord($arr[$idx]);
      $ord++;
      $arr[$idx] = chr($ord);
    }
  }
  return $arr;
}

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