<?php

$alias_string = "AA,BB,CC,";
$alias_extra = "";
if (strlen($alias_string) > 0) {
    $pieces = explode(",", $alias_string);
    $count_item = count($pieces);
    for ($ii = 0; $ii < $count_item; $ii++) {
        $this_element = trim(strtolower($pieces[$ii]));
        if (strlen($this_element) > 0) {
            $itm_str = "'" . $this_element . "'";
            if ($ii > 0) {
                $alias_extra .= ",";
            }
            $alias_extra .= $itm_str;
        }
    }
}


echo $alias_extra;