$user = $_POST['user'];
            $pass = $_POST['pass'];

            $sql1 = "SELECT customerUserName, customerPassword FROM customer
                      WHERE customerUserName = '$user' AND customerPassword = '$pass' ";
            $sql2 = "SELECT staffUserName, staffPassword FROM staff
                      WHERE staffUserName = '$user' AND staffPassword = '$pass' ";
            $sql3 = "SELECT customerID FROM customer WHERE customerUserName = '$user'
                      AND customerPassword = '$pass' ";
            $sql4 = "SELECT staffID FROM staff WHERE staffUserName = '$user'
                      AND staffPassword = '$pass' ";
            $result1 = $conn->query($sql1);
            $result2 = $conn->query($sql2);
            $result3 = $conn->query($sql3);
            $result4 = $conn->query($sql4);
            if ($result1->num_rows > 0) {
                header("Location: custHome.php");
                session_start();
                $_SESSION["userID"] = $result3;

            } else if ($result2->num_rows > 0) {
                header("Location: staffHome.php");
                session_start();
                $_SESSION["adminID"] = $result4;
            }

//new page

<?php
          session_start();
          echo $_SESSION["userID"];
         ?>