<?php
$servername = "localhost";
$username = "root";
$password = "Vikas5914";
$dbname = "test";
// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

$reg_no;
$view_users_query = "SELECT id FROM reg_form ORDER BY id DESC LIMIT 1"; //select query for viewing users.
$result = mysqli_query($conn, $view_users_query); //here run the sql query.
$result = mysqli_fetch_row($result);

$last_id = $result[0];
$reg_no = "MM" . ($last_id + 1000);

$sql = "INSERT INTO reg_form (name, class, reg_no)
VALUES ('John', 'Doe', '$reg_no')";
if (mysqli_query($conn, $sql)) {
    $last_id = mysqli_insert_id($conn);
    echo "Log_ID: " . $last_id = "MM" . ($last_id + 1000);
} else {
    echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}
mysqli_close($conn);
?>