mysqli_real_escape_string() 需要 2 个参数，1 个给定致命错误

I keep getting this errors and I am having problems fixing that, am not good in PHP because am still learning. I am working on a registration form and am using PHP 5.6. I have looked at other answers on older questions but I haven't succeeded.

这是我的代码:

<?php
session_start();
if (isset($_SESSION['user']) != "") {
    header("Location: index.html");
}
include_once 'dbconnect.php';

if (isset($_POST['signup'])) {
    $fname  = mysqli_real_escape_string($_POST['fullname']);
    $tphone = mysqli_real_escape_string($_POST['telephone']);
    $uemail = mysqli_real_escape_string($_POST['email']);
    $urole  = mysqli_real_escape_string($_POST['role']);
    $upass  = md5(mysqli_real_escape_string($_POST['upass']));
    
    $uname  = trim($uname);
    $tphone = trim($tphone);
    $email  = trim($email);
    $urole  = trim($role);
    $upass  = trim($upass);
    
    // email exist or not
    $query  = "SELECT email FROM users WHERE email='$uemail'";
    $result = mysqli_query($query);
    
    $count = mysqli_num_rows($result); // if email not found then register
    
    if ($count == 0) {
        
        if (mysqli_query("INSERT INTO users(firstname,telephone,email,role,pass) VALUES('$fname','$tphone','$uemail','$urole',$upass')")) {
?>
           <script>alert('successfully registered ');</script>
            <?php
        } else {
?>
           <script>alert('error while registering you...');</script>
            <?php
        }
    } else {
?>
           <script>alert('Sorry Email ID already taken ...');</script>
            <?php
    }
    
}
?> 

我不断收到的错误是:

警告:mysqli_real_escape_string() 需要 2 个参数，1 个在 C:Apache24htdocsTimewiselandinglogin.php 第 12 行

header("Location: index.html");
exit;