<?php

class DB extends PDO
{
    // объявление свойства
    protected $host = 'localhost';
    protected $db =   'dfgdfgdfgdfg';  // имя базы
    protected $charset = 'utf8';
    protected $user = 'dfgdfgdfg';       //  имя юзера
    protected $pass = 'dfgdfgdfg';  //  пароль юзера

    function __construct()
    {
        $dsn = "mysql:host=$this->host;dbname=$this->db;charset=$this->charset";
        $opt = [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
        ];
        parent::__construct($dsn, $this->user, $this->pass, $opt);
    }
    public function checkDoubleMail($table, $column, $email) {
        // Проверим есть ли такой юзер
        $auth = $this->prepare('SELECT COUNT(*) FROM `'.$table.'` WHERE `'.$column.'`=:mail');
        $auth->bindParam(':'.$column, $email, PDO::PARAM_STR);
        $auth->execute();
        $Count = $auth->fetchAll();
        return intval(implode('', $Count[0]));
    }
}

class Validator extends DB
{
    public function checkUnique($table, $column, $email)
    {
        $auth = $this->prepare('SELECT COUNT(*) FROM `'.$table.'` WHERE `'.$column.'`=:mail');
        $auth->bindParam(':'.$column, $email, PDO::PARAM_STR);
        $auth->execute();
        $Count = $auth->fetchAll();
        return intval(implode('', $Count[0]));
    }
}

$obj = new DB();
echo '<pre>'; var_dump($obj); echo '</pre>';

$val = new Validator($obj);
$check = $val->checkUnique('users', 'mail', 'mail@yandex.ru');
echo '<pre>'; var_dump($check); echo '</pre>';