用于将用户重定向到空表单页面的php会话

i'm new to php and got a problem with php session. i have a form and when the user press submit button, i want to show an alert, then redirect it to the empty form page. but my code doesn't work:

session_start();

if (mysqli_query($connection, $sql)) {

if (isset($_SESSION['id'])) {
    echo "Records added successfully.";
    header("Location: index.php");
    exit();
} else {
    echo "ERROR: Could not able to execute $sql." . mysqli_error($connection));
    header("Location: index.php");

}

Alert is a javascript function.

If you want to show a Javascript aler you can use this code:

echo '<script>alert("Records added successfully.")</script>';

But in you case if you will show alert page redirect will not work.

If you want to show a success message on index.php page then store that message into session like $_SESSION['message'].

On index.php page check if session contains message then show message and remove it from session, so it can it not appear again. e.g:

if(isset($_SESSION['message'])){
  echo $_SESSION['message'];
  unset($_SESSION['message']);
}