private function commonQuery()
 {
     $sql = "SELECT COUNT(*) FROM `{$this->table}` WHERE {$this->field} =:v";
     $db = Validator::getPDO();
     $stmt = $db->prepare($sql);
     $stmt->bindParam(':v', $this->value, PDO::PARAM_STR);
     $stmt->execute();
     return $stmt;
 }