akamap

$set = [];
while ($can = mysqli_fetch_assoc($res)) {
    if ($set[$can['a']] && $can['c'] == 93) {
         $set[$can['a']]['d'] = $can['d'];
       } elseif (empty($set[$can['a']])) {
         $set[$can['a']] = $can;
    } 
}