Different user login problem because of the syntax error [closed]

In my program, I want different users to have different class_id in order to let them go into different mange page. I distribute them in 3 class id 1= manger 2= NormalUser 3 =admin but when I full outer join them I think the error is here. but i can’t find it can someone help?

the problem is in query

<?php session_start();?>
<?php
include("conn.php");
?>
<?php
if(isset($_POST['submit']))
{
        $user=$_POST['username'];
        $pwd=$_POST['password'];
        $query="SELECT * 
            FROM employees 
            FULL OUTER JOIN admin 
                on employees.class_id=admin.class_id 
            WHERE (employees.employee_id='$user'&& employees.password='$pwd')
              ||(admin.username='$user' && admin.password='$pwd')";
        $data   = mysqli_query($conn,$query);
        $total  =mysqli_num_rows($data);
        $class = $data->fetch_assoc();
        if ($class['class_id']==2)
        {
            $_SESSION['employee_id']=$user;
            header('location:home.php');
        }
        elseif ($class['class_id']==1){
            $_SESSION['employee_id']=$user;
            header('location:manger/home.php');
        } 
        else {
            header('location:index.php');
       }
}

?>

Answer

the problem is here :

use ‘AND’,’OR’ instead of &&,||

WHERE (employees.employee_id='$user' AND employees.password='$pwd')
OR (admin.username='$user' AND admin.password='$pwd')"