SQL PDO计数带有3个参数的行

I have the following code:

 public static function check($ip,$op,$page)
 {
$con = new PDO(DBN,DB_USER,DB_PASS);
$sql = "SELECT COUNT(*) FROM ips WHERE ip=:ip";
$st = $con->prepare($sql);

$st->bindValue(":ip",$ip,PDO::PARAM_STR);


$st->execute();

$counter = $st->fetchColumn();

 $con  = null;
 return $counter;

  }

The $counter display the correct number of rows but if I add

       $st->bindValue(":op",$op,PDO::PARAM_INT);
       $st->bindValue(":page",$page,PDO::PARAM_INT);

$counter appear boolean false; I double checked my DB but every thing there is fine.I tried to add one of them and the other one but the problem persist;

You can activate the PDO debug and see if there's something wrong with your query:

$con->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);