Show DevBest phpacadamy php error help

[Unidentified]

i have been following phpacademy's tutorial for a login + register script and came apon these errors in users.php can someone help

Warning: mysql_result() expects parameter 1 to be resource, boolean given in F:\xampp\htdocs\core\functions\users.php on line 5

Warning: mysql_result() expects parameter 1 to be resource, boolean given in F:\xampp\htdocs\core\functions\users.php on line 5

<?php
   
    function user_exists($email) {
        $email = sanitize($email);
        return (mysql_result(mysql_query("SELECT COUNT ('id') FROM ('usersystem') WHERE 'email' = '$email'"), 0)) ? true : false;
   
   
    }
 
?>

 

[whyherro]

function user_exists($username)
{
$username = sanitize($username);
return (mysql_result(mysql_query("SELECT COUNT(`user_id`) FROM `users` WHERE `username` = '$username'"), 0) == 1) ? true : false;
 
}

Try that