DatabaseNewWay.php

<?php
  // Could have broken request clauses line by line
  // SELECT X FROM Y WHERE Z 
  // ->
  // SELECT X
  // FROM Y
  // WHERE Z
 
  final class RequestHolder {
      // Query a list of users without ordering
      const USERS = 'SELECT * FROM USERS';
      
      // Query all the messages of a user identified by @id_user, ordered by sending date
      const USER_MESSAGES = 'SELECT * FROM Messages WHERE id_user = ? ORDER BY date_sent';
    
      // And so on
      // ...
    
      private function __construct(){
          // Stuff
      }
  }
  
  $this->db->query(RequestHolder.USERS); 

  $this->db->query(RequestHolder.USER_MESSAGES, array('id_user' => 58));
  
?>