php - Memcache & Mysqli prepared statement problem -

check code below, have following problem: last 2 parameters dynamic in sql statement, how can make memcache gets right parameters , not ? ?, shows me only? adding second variable $sql1 = "select id title vtext tpost order id desc limit $var1, $var2"; ? or gives better solution?

$sql = "select id, title, vtext tpost order id desc limit ?, ?"; $content = $memcache->get($sql);  if($content == null) {     $stmt = $mysqli->prepare($sql);     $stmt->bind_param('ii', $offset, $rowsperpage);     $stmt->execute();     $stmt->bind_result($r_id, $r_title, $r_vtext);      while ($stmt->fetch()) {         $data[] = array( 'id' => $r_id, 'title' => $r_title, 'vtext' => $r_vtext);     }     $stmt->close();       $memcache->set($sql,$data,0,$cache_time);  } 

thank help

$sql = "select id, title, vtext tpost order id desc limit ?, ?"; $key = "select id, title, vtext tpost order id desc limit $r_title, $r_vtext"; $content = $memcache->get($sql);  if($content == null) {  $stmt = $mysqli->prepare($sql);  $stmt->bind_param('ii', $offset, $rowsperpage);  $stmt->execute();  $stmt->bind_result($r_id, $r_title, $r_vtext);   while ($stmt->fetch()) {     $data[] = array( 'id' => $r_id, 'title' => $r_title, 'vtext' => $r_vtext);  }  $stmt->close();    $memcache->set($key,$data,0,$cache_time);  }