In this example i am going to show you how to generate randomly alphanumeric string OR number in PHP. when you need you generate random alphanumeric string for your unique field then you can easily create using substr(), md5(), rand(), uniqid(), mt_rand(), time() and str_shuffle() php function you can create several way unique code using following example:
Example
Example 1
$generated = substr(md5(rand()),0,5);
print_r($generated);
Example 2
$generated = rand(10000,99999);
print_r($generated);
Example 3
$generated = substr(md5(uniqid(rand(), true)),0,5);
print_r($generated);
Example 4
$generated = substr(time(),5);
print_r($generated);
Example 5
$generated = substr(str_shuffle(md5(time())),0,5);
print_r($generated);
Example 6
$generated = substr( "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" ,mt_rand( 0 ,50 ) ,2 ) .substr( md5( time() ), 1,3);
print_r($generated);