Generate random unique value in php

<?php
function random_code()
{
    $string = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz0123456789";
    $randval = '' ;

    for($i = 0;$i <= 10;$i++)
    {
        $num = rand() % 62;
        $tmp = substr($string, $num, 1);
        $randval = $randval.$tmp;
    }
    
    echo $randval.uniqid(true);
}
random_code();