a function to get column index by letter  
 
function getColumnNumber($char){
    $alphabet = range('a','z');
    $alphabet2 = range('a','z');
    $newAlphabet = $alphabet;
    foreach($alphabet as $k => $r)
    {
        foreach($alphabet2 as $row){
            $newAlphabet[] = $r.$row;
        }
    }
    $key = array_search($char, $newAlphabet);
    return ($key !== false) ? $key : null;
}