<?php
        if (isset($_POST['login']))
            {
                $username=$_POST['username'];
                $password=$_POST['password'];

                $query= "select * from username WHERE username='$username' AND password='$password' ";

                $query_run = mysqli_query($con,$query);

                if(mysqli_num_rows($query_run)>0)
                {
                    //valid
                    $_SESSION['username']= $username;
                    header('location:homepage.php');
                }
                else {
                    //invalid
                    echo '<script type="text/javascript"> alert ("Invalid credentials") </script>';
                }
            }


        ?>