<?php
/* page access */

$page_access = ['admin','reseller'];
if (!in_array($_SESSION['user_role'], $page_access)) {
    // $user cannot access this page, I should give warning or redirect to somewhere else
    // die('Error: Unauthorized Access');
}

/* data access */

function get($data_id) {
    if ($_SESSION['user_role'] == 'admin') {
        $sql = "SELECT * FROM 'table' WHERE `data_id` = {$data_id}";
    }
    if ($_SESSION['user_role'] == 'user') {
        $sql = "SELECT * FROM 'table' WHERE `username` = '" . $_SESSION['username'] . "' AND `data_id` = {$data_id}";
    }
}