How to make a login form using PHP and MY SQL

<?php

include "databaseconnectivity.php";



mysqli_select_db($con,"login_form");



if(isset($_POST['username']))

{

$u_name = $_POST['username'];

$_password = $_POST['Password'];





$sql = "select * from login where ad_name='".$u_name."'  And ad_password='".$_password."' limit 1";



$result = mysqli_query($con,$sql);



if(mysqli_num_rows($result)==1)

{



echo "<script> alert('Login Successfull') </script>";

exit();

}

else

{

echo "<script> alert('Invalid Name or password') </script>";

exit();



}



}