I'm a beginner, can you explain if I'm using pdo correctly and handling errors?

Question

PHP

Good day fellow developers. I used to use mysql then switched to mysqli, when I found out that in php 7 mysqli was removed, I had to deal with pdo.
What will be better?

<?php
  define('HOST_DB', 'localhost');
  define('USER_DB', 'User');
  define('PASS_DB', 'pass');
  define('NAME_DB', 'db');

define('OPTIONS_DB', 'mysql:host=localhost; dbname=name_db; charset=utf8');
  define('USER_DB', 'User');
  define('PASS_DB', 'pass');

<?php
  define('HOST_DB', 'localhost');
  define('USER_DB', 'User');
  define('PASS_DB', 'pass');
  define('NAME_DB', 'db');
        define('CHARSET_DB', 'utf8');

<?php
  class Database{
    public $db;
    public function __construct($host_db, $user_db, $pass_db, $name_db){
                        //Правильно ли передавать параметры констант в переменных?
      try{
        $this -> db = new PDO("mysql:host=$host_db; dbname=$name_db; charset=utf8", $user_db, $pass_db);
      }
      catch(PDOException $error){
                                  //Запись ошибок в log
        exit('Не удалось подключиться к базе данных!');
      }
      return $this -> db;
    }
    public function get_all_db(){
      $sql = "SELECT `articles_id`, `title`, `keywords`, `description` FROM `articles`";
      $result = $this -> db -> query($sql);
      if(!$result){
        return FALSE;
      }
      for($i = 0; $i < count($result); $i++){ // Возвращает 1 пробовал mysql_num_rows норм отрабатывала //$result -> rowCount(); возвращает правильно 12
        $row[] = $result -> fetchAll(PDO::FETCH_ASSOC);
      }
      return $row;
    }
    public function get_one_db(){
      
    }
  }

but creates an additional multidimensional array(
$result -> rowCount()

if(!$result){
        return FALSE;
      }
      for($i = 0; $i < $result -> rowCount(); $i++){
        $row[] = $result -> fetchAll(PDO::FETCH_ASSOC);
      }
      return $row;
Array
(
    [0] => Array
        (
            [0] => Array
                (
                    [articles_id] => 1
                    [title] => Как правильно использовать теги div, section и article.
                    [keywords] => 
                    [description] => 
                )

            [1] => Array
                (
                    [articles_id] => 2
                    [title] => Валидность HTML-кода
                    [keywords] => 
                    [description] => 
                )

            [2] => Array
                (
                    [articles_id] => 3
                    [title] => HTML 5 Что нового?
                    [keywords] => 
                    [description] => 
                )

            [3] => Array
                (
                    [articles_id] => 4
                    [title] => CSS
                    [keywords] => 
                    [description] => 
                )

            [4] => Array
                (
                    [articles_id] => 5
                    [title] => Сокрытие элементов на CSS.
                    [keywords] => 
                    [description] => 
                )

            [5] => Array
                (
                    [articles_id] => 6
                    [title] => JavaScript
                    [keywords] => 
                    [description] => 
                )

            [6] => Array
                (
                    [articles_id] => 7
                    [title] => Как визуализировать графики и сделать их интерактивными на JavaScript.
                    [keywords] => 
                    [description] => 
                )

            [7] => Array
                (
                    [articles_id] => 8
                    [title] => PHP
                    [keywords] => 
                    [description] => 
                )

            [8] => Array
                (
                    [articles_id] => 9
                    [title] => Что нового в PHP7.1: генерация случайных чисел.
                    [keywords] => 
                    [description] => 
                )

            [9] => Array
                (
                    [articles_id] => 10
                    [title] => Социальная сеть на PHP: вывод домашней страницы.
                    [keywords] => 
                    [description] => 
                )

            [10] => Array
                (
                    [articles_id] => 11
                    [title] => jQuery
                    [keywords] => 
                    [description] => 
                )

            [11] => Array
                (
                    [articles_id] => 12
                    [title] => Ajax запросы с помощью методов $.post() и $.get().
                    [keywords] => 
                    [description] => 
                )

        )

    [1] => Array
        (
        )

    [2] => Array
        (
        )

    [3] => Array
        (
        )

    [4] => Array
        (
        )

    [5] => Array
        (
        )

    [6] => Array
        (
        )

    [7] => Array
        (
        )

    [8] => Array
        (
        )

    [9] => Array
        (
        )

    [10] => Array
        (
        )

    [11] => Array
        (
        )

)

Whether it is correct if to throw in parameters the following?

<?php
  $host = '127.0.0.1';
    $db   = 'test';
    $user = 'root';
    $pass = '';
    $charset = 'utf8';

    $dsn = "mysql:host=$host;dbname=$db;charset=$charset";
    $opt = [
        PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
        PDO::ATTR_EMULATE_PREPARES   => false,
    ];
    $pdo = new PDO($dsn, $user, $pass, $opt);

  try {
    $dbh = new PDO($dsn, $user, $password);
  } catch (PDOException $e) {
    die('Подключение не удалось: ' . $e->getMessage());
  }
  
  $stmt = $pdo->query('SELECT name FROM users');
  while ($row = $stmt->fetch())
  {
    echo $row['name'] . "\n";
  }

Answer 1

No, everything is wrong here.
In short, then
1. Throw the Database class in the trash.
2. Throw all exit() in the code in the trash
3. All try..catch there
As a result, we will have

class article {
    public function __construct($pdo)
        $this->pdo = $pdo;
    }
    public function get_all_db() {
        $sql = "SELECT `articles_id`, `title`, `keywords`, `description` FROM `articles`";
        return $this->pdo->query($sql)->fetchAll();
    }
    public function get_one_db($id){
        $sql = "SELECT `articles_id`, `title`, `keywords`, `description` FROM `articles` WHERE articles_id = ?";
        $stmt = $this->pdo->prepare($sql);
        $stmt->execute([$id]);
        return $stmt->fetch();
    }
}

Everything is convenient, compact and safe.
There is less code than in mysqli and mysql combined.