Создаем модель

<?php

class WorkerModel {

    public function __construct() {
        $this->db = mysqli_connect('localhost','root','',"world_db");

    }

    public function getWorkers() {
        $query = "SELECT *
                  FROM workers
                  ";

        $result = $this->db->query($query);
        return $result->fetch_all();
    }
}

?>