IDs are often numbers. Unfortunately there are only 10 digits to work with, so if you have a lot of records, IDs tend to get very lengthy. For computers that's OK. But human beings like their IDs as short as possible. So how can we make IDs shorter? Well, we could borrow characters from the alphabet as have them pose as additional numbers.... Alphabet to the rescue!

Other title options where

• How to create unique short string IDs with PHP & MySQL
• Or how to create IDs similar to YouTube e.g. yzNjIBEdyww

I created this function a long time ago. Time to be nice and share.

More is Less - the 'math'

The alphabet has 26 characters. That's a lot more than 10 digits. If we also distinguish upper- and lowercase, and add digits to the bunch or the heck of it, we already have (26 x 2 + 10) 62 options we can use per position in the ID.

Now of course we can also add additional funny characters to 'the bunch' like - / * & #  but those may cause problems in URLs and that's our target audience for now.

OK so because there are roughly 6x more characters we will use per position, IDs will get much shorter. We can just fit a lot more data in each position.

This is basically what url shortening services do like tinyurl, is.gd, or bit.ly. But similar IDs can also be found at youtube: http://www.youtube.com/watch?v=yzNjIBEdyww

Convert your IDs

Now unlike Database servers: webservers are easy to scale so you can let them do a bit of converting to ease the life of your users, while keeping your database fast with numbers (MySQL really likes them plain numbers ; ).

To do the conversion I've written a PHP function that can translate big numbers to short strings and vice versa. I call it: alphaID.

The resulting string is not hard to decipher, but it can be a very nice feature to make URLs or directorie structures more compact and significant.

So basically:

• when someone requests rLHWfKd
• alphaID() converts it to 999999999999
• you lookup the record for id 999999999999 in your database

Source

<?php
/**
 * Translates a number to a short alhanumeric version
 *
 * Translated any number up to 9007199254740992
 * to a shorter version in letters e.g.:
 * 9007199254740989 --> PpQXn7COf
 *
 * specifiying the second argument true, it will
 * translate back e.g.:
 * PpQXn7COf --> 9007199254740989
 *
 * this function is based on any2dec && dec2any by
 * fragmer[at]mail[dot]ru
 * see: http://nl3.php.net/manual/en/function.base-convert.php#52450
 *
 * If you want the alphaID to be at least 3 letter long, use the
 * $pad_up = 3 argument
 *
 * In most cases this is better than totally random ID generators
 * because this can easily avoid duplicate ID's.
 * For example if you correlate the alpha ID to an auto incrementing ID
 * in your database, you're done.
 *
 * The reverse is done because it makes it slightly more cryptic,
 * but it also makes it easier to spread lots of IDs in different
 * directories on your filesystem. Example:
 * $part1 = substr($alpha_id,0,1);
 * $part2 = substr($alpha_id,1,1);
 * $part3 = substr($alpha_id,2,strlen($alpha_id));
 * $destindir = "/".$part1."/".$part2."/".$part3;
 * // by reversing, directories are more evenly spread out. The
 * // first 26 directories already occupy 26 main levels
 *
 * more info on limitation:
 * - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372
 *
 * if you really need this for bigger numbers you probably have to look
 * at things like: http://theserverpages.com/php/manual/en/ref.bc.php
 * or: http://theserverpages.com/php/manual/en/ref.gmp.php
 * but I haven't really dugg into this. If you have more info on those
 * matters feel free to leave a comment.
 * 
 * @author    Kevin van Zonneveld <kevin@vanzonneveld.net>
 * @author    Simon Franz
 * @author    Deadfish
 * @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)
 * @license   http://www.opensource.org/licenses/bsd-license.php New BSD Licence
 * @version   SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $
 * @link      http://kevin.vanzonneveld.net/
 * 
 * @param mixed   $in      String or long input to translate
 * @param boolean $to_num  Reverses translation when true
 * @param mixed   $pad_up  Number or boolean padds the result up to a specified length
 * @param string  $passKey Supplying a password makes it harder to calculate the original ID
 * 
 * @return mixed string or long
 */
function alphaID($in, $to_num = false, $pad_up = false, $passKey = null)
{
    $index = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    if ($passKey !== null) {
        // Although this function's purpose is to just make the
        // ID short - and not so much secure,
        // with this patch by Simon Franz (http://blog.snaky.org/)
        // you can optionally supply a password to make it harder
        // to calculate the corresponding numeric ID
        
        for ($n = 0; $n<strlen($index); $n++) {
            $i[] = substr( $index,$n ,1);
        }
 
        $passhash = hash('sha256',$passKey);
        $passhash = (strlen($passhash) < strlen($index))
            ? hash('sha512',$passKey)
            : $passhash;
 
        for ($n=0; $n < strlen($index); $n++) {
            $p[] =  substr($passhash, $n ,1);
        }
        
        array_multisort($p,  SORT_DESC, $i);
        $index = implode($i);
    }
 
    $base  = strlen($index);
 
    if ($to_num) {
        // Digital number  <<--  alphabet letter code
        $in  = strrev($in);
        $out = 0;
        $len = strlen($in) - 1;
        for ($t = 0; $t <= $len; $t++) {
            $bcpow = bcpow($base, $len - $t);
            $out   = $out + strpos($index, substr($in, $t, 1)) * $bcpow;
        }
 
        if (is_numeric($pad_up)) {
            $pad_up--;
            if ($pad_up > 0) {
                $out -= pow($base, $pad_up);
            }
        }
        $out = sprintf('%F', $out);
        $out = substr($out, 0, strpos($out, '.'));
    } else { 
        // Digital number  -->>  alphabet letter code
        if (is_numeric($pad_up)) {
            $pad_up--;
            if ($pad_up > 0) {
                $in += pow($base, $pad_up);
            }
        }
 
        $out = "";
        for ($t = floor(log($in, $base)); $t >= 0; $t--) {
            $bcp = bcpow($base, $t);
            $a   = floor($in / $bcp) % $base;
            $out = $out . substr($index, $a, 1);
            $in  = $in - ($a * $bcp);
        }
        $out = strrev($out); // reverse
    }
 
    return $out;
}
?>

Example

Running:

alphaID(9007199254740989);

will return 'PpQXn7COf' and:

alphaID('PpQXn7COf', true);

will return '9007199254740989'

Easy right?

More features

• There also is an optional third argument: $pad_up. This enables you to make the resulting alphaId at least X characters long.
• You can support even more characters (making the resulting alphaID even smaller) by adding characters to the $index var at the top of the function body.

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